xm-85h50ai: turn on majestic's autofocus out of the box (#142)

The first camera with working autofocus on HiSilicon: the customizer
enables majestic's contrast AF engine (widgetii/majestic#522), which
reads the ISP's BE AF zone statistics and drives this board's XM zoom
block over the same UART the pad uses, serialised by the same lock.
The engine defaults to off everywhere — a lens without a focus motor
must not grow an /autofocus endpoint — so enabling it in the profile
of the board it was proven on is the whole change; port and speed
defaults already match. The WebUI grows an AF button and books a
settle-gated pass after each zoom step (majestic-webui#265).

Verified end to end on the lab unit: from total blur to a tack-sharp
frame, fv 30 -> 5126 against a 5606 peak in 21s.

devices/hi3516ev300_lite_xm-85h50ai/general/overlay/usr/share/openipc/customizer.sh

@@ -25,6 +25,12 @@ fw_setenv ptz_port /dev/ttyAMA0
 fw_setenv ptz_caps 'zoom focus'
 #
 #
+# Autofocus: majestic's contrast AF engine over the ISP focus statistic,
+# driving the same zoom block. Default port/speed already match this board.
+#
+cli -s .isp.autofocus.enabled true
+#
+#
 # The MCU owns the console UART, so getty must not sit on it reading the
 # MCU's bytes. The edit lands in the overlay; an upgrade that wipes the
 # overlay also wipes /etc/custom.ok, so this script runs again and the