mtd: rawnand: Drop obsolete JZ4740 NAND driver

It has been replaced with the newer Ingenic NAND driver.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Tested-by: Artur Rojek <contact@artur-rojek.eu>
Acked-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>