mtd: spi-nor: atmel-quadspi: add suspend/resume hooks

Implement suspend/resume hooks.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>