Plane: check for APPDIR to pull in px4 build logic

ArduPlane/Makefile

@@ -1,5 +1,22 @@
+
+ifeq ($(APPDIR),)
+####################
+# AVR and SITL build
 include ../mk/Arduino.mk
 include ../mk/targets.mk
 
 sitl-newcontrollers: EXTRAFLAGS += "-DAPM_CONTROL=ENABLED "
 sitl-newcontrollers: sitl
+
+else
+
+####################
+# PX4 build
+APPNAME		 = ArduPlane
+PRIORITY	 = SCHED_PRIORITY_DEFAULT
+STACKSIZE	 = 4096
+
+SKETCHBOOK=..
+include $(APPDIR)/mk/apm.mk
+
+endif