mtd: spinand: Add initial support for Winbond W25M02GV

Add support for the W25M02GV chip.

Signed-off-by: Frieder Schrempf <frieder.schrempf@exceet.de>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>