Adding DurioSound Driver On branch rpi-3.12.y

Changes to be committed:
	new file:   sound/soc/bcm/duriosound-dac.c
	modified:   arch/arm/configs/bcmrpi_defconfig
	modified:   arch/arm/mach-bcm2708/bcm2708.c
	modified:   sound/soc/bcm/Kconfig
	modified:   sound/soc/bcm/Makefile