airoha: increase the size of reserved_bmt partition

airoha: increase the size of reserved_bmt partition

The vendor firmware checks for a bmt header in the last 528 erase blocks
of flash. The OpenWrt partition table did not respect that requirement,
and therefore the vendor and openwrt chainloader fight over those blocks
on every boot, potentially corrupting data stored in UBI blocks there.
This commit increases the size of the reserved_bmt partition to avoid
that fight.

Although the vendor bootloader only seems to touch the final 250 erase
blocks[1], the original vendor firmware system partition ended at
0x1be00000[2], so to be conservative, the consensus is to use that as
the end of mtd2 (ubi) partition and leave the last 528 blocks for mtd3
(reserved_bmt).

From https://openwrt.org/toh/gemtek/mxf-w1700k:
[1] OEM bootlog: [    5.324337] bmt pool size: 250
[2] OEM bootlog: [    5.478927] 0x000008600000-0x00001be00000 : "system"

Adds a compat_version to warn users to re-install to accomodate the
shrunken mtd2 ubi partition.

Fixed two nits suggested by Claude, zero padding a hex value and removed
an extra space.

Removed the wildcard setting of compat_version for other boards, as
suggested by Robert Marko, set compat_version only for the w1700k.

Reported-by: Loïc Yhuel <loic.yhuel@gmail.com>
Signed-off-by: Russell Senior <russell@personaltelco.net>
Link: https://github.com/openwrt/openwrt/pull/23061
Signed-off-by: Robert Marko <robimarko@gmail.com>