brcm2708: convert to metadata

This patch converts all the raspberrypi images to utilize
the common metadata-based image verification.

Note: the CM1 and CM3 currently use the same "rpi-cm"
boardname.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>

target/linux/brcm2708/base-files/lib/upgrade/platform.sh

@@ -1,20 +1,7 @@
-get_magic_at() {
-	local file="$1"
-	local pos="$2"
-	get_image "$file" | dd bs=1 count=2 skip="$pos" 2>/dev/null | hexdump -v -n 2 -e '1/1 "%02x"'
-}
+REQUIRE_IMAGE_METADATA=1
 
 platform_check_image() {
-	local file="$1"
-	local magic
-
-	magic=$(get_magic_at "$file" 510)
-	[ "$magic" != "55aa" ] && {
-		echo "Failed to verify MBR boot signature."
-		return 1
-	}
-
-	return 0;
+	return 0
 }
 
 platform_do_upgrade() {

target/linux/brcm2708/image/Makefile

@@ -50,13 +50,14 @@ define Device/Default
   FILESYSTEMS := ext4
   KERNEL := kernel-bin | kernel-img
   KERNEL_IMG := kernel.img
-  IMAGES := sdcard.img
-  IMAGE/sdcard.img := boot-img | sdcard-img
+  IMAGES := sdcard.img.gz
+  IMAGE/sdcard.img.gz := boot-img | sdcard-img | gzip | append-metadata
 endef
 
 define Device/rpi
   DEVICE_TITLE := Raspberry Pi B/B+/CM/Zero/ZeroW
   DEVICE_DTS := bcm2708-rpi-b bcm2708-rpi-b-plus bcm2708-rpi-cm bcm2708-rpi-0-w
+  SUPPORTED_DEVICES := rpi-b rpi-b-plus rpi-cm rpi-zero-w
 endef
 ifeq ($(SUBTARGET),bcm2708)
   TARGET_DEVICES += rpi
@@ -65,6 +66,7 @@ endif
 define Device/rpi-2
   DEVICE_TITLE := Raspberry Pi 2B/3B/3CM
   DEVICE_DTS := bcm2709-rpi-2-b bcm2710-rpi-3-b bcm2710-rpi-cm3
+  SUPPORTED_DEVICES := rpi-2-b rpi-3-b rpi-cm
 endef
 ifeq ($(SUBTARGET),bcm2709)
   TARGET_DEVICES += rpi-2
@@ -74,6 +76,7 @@ define Device/rpi-3
   KERNEL_IMG := kernel8.img
   DEVICE_TITLE := Raspberry Pi 3B (64 bit)
   DEVICE_DTS := broadcom/bcm2710-rpi-3-b
+  SUPPORTED_DEVICES := rpi-3-b
 endef
 ifeq ($(SUBTARGET),bcm2710)
   TARGET_DEVICES += rpi-3