mtd: spinand: Add initial support for Micron MT29F2G01ABAGD

Add a basic driver for Micron SPI NANDs. Only one device is supported
right now, but the driver will be extended to support more devices
afterwards.

Signed-off-by: Peter Pan <peterpandong@micron.com>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>