fpv: give the 8812eu its own gk7205v200 build (#133)

#61 asks for 8812eu support on gk7205v200 FPV. #70 and the first version of this PR
both tried to satisfy it by adding BR2_PACKAGE_RTL88X2EU_OPENIPC=y next to the existing
BR2_PACKAGE_RTL8812AU_OPENIPC=y. CI built that and it does not fit:

    - uImage:          [1988KB/2048KB]
    - rootfs.squashfs: [5504KB/5120KB]
    -- size exceeded by: 384KB

Two heavy kernel Wi-Fi drivers do not go in one 8M image. The driver itself is fine --
8812eu.ko links and installs -- it is purely flash budget, and there is no 384KB of
slack in a 5MB rootfs that was already at its cap.

The tree had already said so. Every defconfig here that ships both drivers is 16M: the
ssc338q, ssc30kq, ssc377qe and ssc378qe fpv/apfpv/rubyfpv targets. Every 8M one ships
8812au alone: gk7205v200/v210/v300 fpv and venc, hi3516ev200_fpv, hi3516ev300_fpv. The
"missing" 8812eu on the Goke configs was never an oversight; it is what 8M allows.

So this is a separate build. gk7205v200_fpv_8812eu is gk7205v200_fpv with one line
changed, the driver swapped rather than added:

    -BR2_PACKAGE_RTL8812AU_OPENIPC=y
    +BR2_PACKAGE_RTL88X2EU_OPENIPC=y

The existing gk7205v200_fpv is untouched, so nobody on an 8812au adapter is affected.
It builds with room to spare -- rootfs 5024KB/5120KB, 96KB headroom.

Nothing else had to move for it:

  - Registration is automatic; the defconfig is the registration. --self-test passes at
    108 devices and the diff narrows to exactly this target, so its own build proved it.
  - Excludes resolve as ${OPENIPC_SOC_MODEL}_${OPENIPC_VARIANT}.list in firmware's
    rootfs_script.sh, and VARIANT stays "fpv", so it reuses gk7205v200_fpv.list. That
    list strips neither driver.
  - Release assets do not collide. master.yml keys on the underscore count:
    gk7205v200_fpv is COMMON=1 and uploads the canonical openipc.gk7205v200-nor-fpv.tgz,
    this one is COMMON=2 and is renamed to gk7205v200_fpv_8812eu-nor.tgz. Same for its
    sizes.json.

Only gk7205v200, which is what #61 asked for. The other four 8M FPV targets have the
same constraint and could take the same treatment if anyone asks.

Closes #70.

devices/common/br-ext-chip-goke/configs/gk7205v200_fpv_8812eu_defconfig

@@ -0,0 +1,63 @@
+# Architecture
+BR2_arm=y
+BR2_cortex_a7=y
+BR2_ARM_EABI=y
+BR2_ARM_FPU_NEON_VFPV4=y
+BR2_ARM_INSTRUCTIONS_THUMB2=y
+
+# Toolchain
+BR2_TOOLCHAIN_EXTERNAL=y
+BR2_TOOLCHAIN_EXTERNAL_DOWNLOAD=y
+BR2_TOOLCHAIN_EXTERNAL_URL="https://github.com/openipc/firmware/releases/download/$(OPENIPC_TOOLCHAIN).tgz"
+BR2_TOOLCHAIN_EXTERNAL_CUSTOM_PREFIX="arm-openipc-linux-musleabi"
+BR2_TOOLCHAIN_EXTERNAL_HEADERS_4_9=y
+BR2_TOOLCHAIN_EXTERNAL_CUSTOM_MUSL=y
+BR2_TOOLCHAIN_EXTERNAL_CXX=y
+
+# Kernel
+BR2_LINUX_KERNEL=y
+BR2_LINUX_KERNEL_CUSTOM_TARBALL=y
+BR2_LINUX_KERNEL_CUSTOM_TARBALL_LOCATION="https://github.com/openipc/linux/archive/$(OPENIPC_KERNEL).tar.gz"
+BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
+BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="$(EXTERNAL_VENDOR)/board/$(OPENIPC_SOC_FAMILY)/gk7205v200.generic-fpv.config"
+BR2_LINUX_KERNEL_UIMAGE=y
+BR2_LINUX_KERNEL_XZ=y
+
+# Filesystem
+BR2_PACKAGE_BUSYBOX_CONFIG="$(BR2_EXTERNAL)/package/busybox/busybox.config"
+BR2_PACKAGE_UBOOT_TOOLS=y
+BR2_PACKAGE_LIBZIP=y
+BR2_PACKAGE_JSON_C=y
+# BR2_PACKAGE_IFUPDOWN_SCRIPTS is not set
+BR2_PACKAGE_WIRELESS_TOOLS=y
+BR2_TARGET_ROOTFS_CPIO=y
+BR2_TARGET_ROOTFS_SQUASHFS=y
+BR2_TARGET_ROOTFS_SQUASHFS4_XZ=y
+
+# OpenIPC
+BR2_OPENIPC_SOC_VENDOR="goke"
+BR2_OPENIPC_SOC_MODEL="gk7205v200"
+BR2_OPENIPC_SOC_FAMILY="gk7205v200"
+BR2_OPENIPC_VARIANT="fpv"
+BR2_OPENIPC_FLASH_SIZE="8"
+BR2_OPENIPC_MAJESTIC="fpv"
+
+# Packages
+BR2_PACKAGE_DROPBEAR_OPENIPC=y
+BR2_PACKAGE_GOKE_OSDRV_GK7205V200=y
+BR2_PACKAGE_HISILICON_OPENSDK=y
+BR2_PACKAGE_IPCTOOL=y
+BR2_PACKAGE_LIBCURL_OPENIPC=y
+BR2_PACKAGE_LIBCURL_OPENIPC_CURL=y
+# BR2_PACKAGE_LIBCURL_OPENIPC_PROXY_SUPPORT is not set
+# BR2_PACKAGE_LIBCURL_OPENIPC_COOKIES_SUPPORT is not set
+# BR2_PACKAGE_LIBCURL_OPENIPC_EXTRA_PROTOCOLS_FEATURES is not set
+BR2_PACKAGE_LINUX_FIRMWARE_OPENIPC=y
+BR2_PACKAGE_MAJESTIC=y
+BR2_PACKAGE_MAVFWD=y
+BR2_PACKAGE_MAVLINK_ROUTER=y
+BR2_PACKAGE_MBEDTLS_OPENIPC=y
+BR2_PACKAGE_RTL88X2EU_OPENIPC=y
+BR2_PACKAGE_VTUND_OPENIPC=y
+BR2_PACKAGE_WIFIBROADCAST=y
+BR2_PACKAGE_YAML_CLI=y