lantiq: add platform_pre_upgrade for sysupgrade

As explained in recent sysupgrade/nand.sh commits, current NAND
sysupgrade is a bit misleading because of nand_do_platform_check
behavior. It leaves a special mark in /tmp/sysupgrade-nand-path
triggering some diffent code path in nand_upgrade_stage1.

The plan is to have the check function only check the image and nothing
else. Then platform code (platform_pre_upgrade) should trigger NAND
specific upgrade path. This is what this patch implements.

Please note that because of current nand_upgrade_stage1 implementation
this patch doesn't change any behaior yet. It only prepares lantiq
target for changing nand_do_platform_check (it will be possible after
preparing all other targets as well).

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>

SVN-Revision: 46939

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

@@ -25,6 +25,16 @@ platform_check_image() {
 	esac
 }
 
+platform_pre_upgrade() {
+	local board=$(lantiq_board_name)
+
+	case "$board" in
+	BTHOMEHUBV2B|BTHOMEHUBV3A|P2812HNUF* )
+		nand_do_upgrade $1
+		;;
+	esac
+}
+
 # use default for platform_do_upgrade()
 
 disable_watchdog() {