mtd: spi-nor: Move Macronix bits out of core.c

Create a SPI NOR manufacturer driver for Macronix chips, and move the
Macronix definitions outside of core.c.

Signed-off-by: Boris Brezillon <bbrezillon@kernel.org>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Tested-by: Xiang Chen <chenxiang66@hisilicon.com>