MIPS: txx9: Move the ndfc.h header to include/linux/platform_data/txx9

This way we will be able to compile the ndfmc driver when
COMPILE_TEST=y.

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>