kernel: nmbm: add mediatek,bmt-mtd-overridden-oobsize property

kernel: nmbm: add mediatek,bmt-mtd-overridden-oobsize property

This commit adds new "mediatek,bmt-mtd-overridden-oobsize" property. The
property helps avoid "NMBM configuration mismatch" error if mtd "OOB size"
is not equal to the "spare size" which is stored in the nmbm signature.

Signed-off-by: Mikhail Zhilkin <csharper2005@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/17549
Signed-off-by: Robert Marko <robimarko@gmail.com>
(cherry picked from commit e585ae70d4f2a563b3b0e430e15ee19ad25caeb5)
Signed-off-by: Mikhail Zhilkin <csharper2005@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/17898
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>