linux-phytec-ti

mtd: nand: add nand_check_erased helper functions

Add two helper functions to help NAND controller drivers test whether a
specific NAND region is erased or not.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>