mtd: spi-nor: Add support for is25wp series chips

Added support for is25wp032, is25wp064 and is25wp128.

Signed-off-by: Kimmo Rautkoski <ext-kimmo.rautkoski@vaisala.com>
Reviewed-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>