dt-bindings: mtd: spi-nor: Add reset-gpios property

SPI-NOR flashes have RESET pin which can be toggled using GPIO
controller, for those platforms reset-gpios property can be used to
reset the flash device.

Signed-off-by: Sai Krishna Potthuri <sai.krishna.potthuri@amd.com>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220908064428.2962-2-sai.krishna.potthuri@amd.com