spi/spi-atmel: add physical base address

Needed for future use with dmaengine enabled driver.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
[wenyou.yang@atmel.com: submit the patch]
Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Tested-by: Richard Genoud <richard.genoud@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>