spi: atmel-quadspi: fix possible MMIO window size overrun

The sama5d2 QSPI controller memory space is limited to 128MB:
0x9000_00000-0x9800_00000/0XD000_0000--0XD800_0000.

There are nor flashes that are bigger in size than the memory size
supported by the controller: Micron MT25QL02G (256 MB).

Check if the address exceeds the MMIO window size. An improvement
would be to add support for regular SPI mode and fall back to it
when the flash memories overrun the controller's memory space.

Fixes: 24c8ff46 ("spi: Add Atmel QuadSPI driver")
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>