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

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

Signed-off-by: Boris Brezillon <bbrezillon@kernel.org>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>