ARM: dts: at91: Disable SPI on at91sam9x5ek to allow MCI1 to work.

The A13 hardware line is shared by SPI and MCI1 controller.This patch
disables the SPI controller so that the MCI1 (the big MMC card slot) can
be used.

Signed-off-by: Cristian Birsan <cristian.birsan@microchip.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>