[Taranis] Asynchronous screenshots (to ensure the LCD will be fully

refreshed before doing the screenshot)

radio/src/main_arm.cpp

@@ -36,8 +36,9 @@
 
 #include "opentx.h"
 
-static uint8_t currentSpeakerVolume = 255;
+uint8_t currentSpeakerVolume = 255;
 uint8_t requiredSpeakerVolume = 255;
+uint8_t requestScreenshot = false;
 
 void handleUsbConnection()
 {
@@ -207,4 +208,11 @@ void perMain()
   bt_wakeup();
 #endif
 
+#if defined(PCBTARANIS)
+  if (requestScreenshot) {
+    requestScreenshot = false;
+    writeScreenshot();
+  }
+#endif
+
 }