This commit corresponds to apache/nuttx#11498 in nuttx.
Move etc romfs mount to sched/init for compatibility with kernel/protected mode.
changes:
- move etc romfs mount from nsh to Nuttx, but keep the script to parse and execute.
- move and rename the related CONFIG, move customized nsh_romfsimg.h to etc_romfs.c
in boards, and no need declaration for romfs_img/romfs_img_len.
Signed-off-by: fangxinyong <fangxinyong@xiaomi.com>
