BMT replaces nand-specific ops for erasing and writing, but the
mtk-snand driver only implements generic mtd api.
Replace erase, block_isbad, block_markbad in mtd_info for generic mtd
drivers.
Fixes: b600aee3ed ("mediatek: attach bmt to the new snand driver")
Signed-off-by: Chuanhong Guo <gch981213@gmail.com>