NuttX build in place

- cmake NuttX build wrapper compile in place instead of copying source tree to build directory
    - slightly faster skipping necessary copying (depending on system)
    - allows debugging in place
    - easier to work directly in NuttX following official documentation
    - simplifies overall build which should make it easier to resolve any remaining NuttX dependency issues in the build system
 - the downside is switching back and forth between different builds always require rebuilding NuttX, but I think this is worth the improved developer experience
 - also no longer builds px4io and bootloader in every single build, for most users these rarely change and we're wasting a lot of build time

ROMFS/px4fmu_common/init.d/rcS

@@ -507,21 +507,13 @@ else
 		. ${R}etc/init.d/rc.autostart.post
 	fi
 
-	#
-	# Bootloader upgrade
-	#
-	if param compare -s SYS_BL_UPDATE 1
+
+	set BOARD_BOOTLOADER_UPGRADE ${R}etc/init.d/rc.board_bootloader_upgrade
+	if [ -f $BOARD_BOOTLOADER_UPGRADE ]
 	then
-		if [ -f "/etc/extras/bootloader.bin" ]
-		then
-			param set SYS_BL_UPDATE 0
-			param save
-			echo "bootloader update..."
-			bl_update "/etc/extras/bootloader.bin"
-			echo "bootloader update done, rebooting"
-			reboot
-		fi
+		sh $BOARD_BOOTLOADER_UPGRADE
 	fi
+	unset BOARD_BOOTLOADER_UPGRADE
 
 #
 # End of autostart.