powerpc/82xx: add SPI support for mgcoge

Add spi support for mgcoge into the platform code and the dts
file. Additionaly SPIDEV is switched on in the defconfig and the
updates for the newer kernel version are committed. The SPI
interface is used to drive the Maxim DS3106 clock chip.

Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
cc: Heiko Schocher <hs@denx.de>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>