mtd: rawnand: Add support for manufacturer specific suspend/resume operation

Patch nand_suspend() & nand_resume() to let manufacturers overwrite
suspend/resume operations.

Signed-off-by: Mason Yang <masonccyang@mxic.com.tw>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/1584517348-14486-2-git-send-email-masonccyang@mxic.com.tw