mtd: rawnand: ingenic: Rename jz4780_nand driver to ingenic_nand

The jz4780_nand driver will be modified to handle all the Ingenic
JZ47xx SoCs that the upstream Linux kernel supports (JZ4740, JZ4725B,
JZ4770, JZ4780), so it makes sense to rename it.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>