mtd: nand: denali: change the setup_dma choice into hook

The previous commit added some hooks into struct denali_nand_info,
so here is one more for clean-up.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>