base-files: filogic: allow sysupgrade compatible profiles

These two profiles are suppose to be compatible with each other since
they are the same device except for the WAN port PHY [1].

They include the other device's dts compatible string in SUPPORTED_DEVICES
in order to allow flashing either image on either device but there is an
implicit constraint in the sysupgrade-TAR images's building script which
hardcode the "image makefile profile name"(DEVICE_NAME or BOARD_NAME if
defined) during the image-building process, but, later on, it is the
"board_name()"(dts compatible) what it is checked in "nand_do_platform_check"
during sysupgrading on device. That implies that only one specific dts
compatible string (the one which match the profile name) will do a
seamless sysupgrade [2].

In order to allow sysupgrade between these two profiles, each one with
its own dts compatible string, we need to relax this check.

Since we use fwtool for image metadata checks (including the
SUPPORTED_DEVICES check for a valid board_name), delegate to fwtool and
avoid "nand_do_platform_check" in this case.

*Git history reflects that using image METADATA is the prefered way to do
this check is using fwtool, so this change is aligned with that trend.

[1]: openwrt#18799 (comment)
[2]: openwrt#20566 (comment)
Fixes(only mediatek-filogic): openwrt#20966
Fixes: openwrt#20566

Signed-off-by: Mario Andrés Pérez <mapb_@outlook.com>

Author: map-b

target/linux/mediatek/filogic/base-files/lib/upgrade/platform.sh

@@ -315,6 +315,11 @@ platform_check_image() {
 			return 1
 		}
 
+		return 0
+		;;
+	glinet,gl-mt2500|\
+	glinet,gl-mt2500-airoha)
+		# delegate on fwtool for image checks to allow cross sysupgrades
 		return 0
 		;;
 	*)