ARM: dts: at91: sam9x60ek: Use quad mode in the spi-nor flash

Both the QSPI controller and the sst26vf064b flash support
quad mode, enable it.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/20200403061222.1277147-1-tudor.ambarus@microchip.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>