mtd: rawnand: jz4780: Drop the dependency on MACH_JZ4780

This MACH_JZ4780 dependency is taken care of by JZ4780_NEMC, no need
to repeat it here.

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Acked-by: Paul Burton <paul.burton@mips.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>