mtd: rawnand: denali: use more nand_chip pointers for internal functions

With the recent refactoring, the NAND driver hooks now take a pointer
to nand_chip. Add to_denali() in order to convert (struct nand_chip *)
to (struct denali_nand_info *) directly. It is more useful than the
current mtd_to_denali().

I changed some helper functions to take (struct nand_chip *). This will
avoid pointer conversion back and forth, and ease further development.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>