mtd: nand: denali: use BIT() and GENMASK() for register macros

Use BIT() and GENMASK() for register field macros.  This will make
it easier to compare the macros with the register description in the
Denali User's Guide.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>