[][OpenWrt Dev][Add option for NMBM to support running in read-only mode]

Add an option to allow NMBM running in read-only where only read operation
is accepted, and write/erase operation will be rejected.

With this option turned on, NMBM will write no signature block nor any
information table into NAND flash, which allows lower write/erase API
not being provided.


Change-Id: Ia6931b073d2d56f722284c0b894e30551cd7c359
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/4672347
2 files changed