ROMFS handle bl_update generically

- include all available legacy bootloaders

ROMFS/px4fmu_common/extras/README.txt

@@ -1,5 +0,0 @@
-px4fmuv3_bl.bin: Bootloader binary of the PX4 Bootloader
-  (https://github.com/PX4/Bootloader)
-  based on commit 184b813699a9cfd6f43a5a21556a06b4372baf5f
-  for the target px4fmuv3_bl
-

ROMFS/px4fmu_common/init.d/rcS

@@ -549,6 +549,22 @@ else
 		. ${R}etc/init.d/rc.autostart.post
 	fi
 
+	#
+	# Bootloader upgrade
+	#
+	if param compare -s SYS_BL_UPDATE 1
+	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
+	fi
+
 	if ! param compare SYS_PARAM_VER ${PARAM_DEFAULTS_VER}
 	then
 		echo "Switched to different parameter version. Resetting parameters."