dts: add support for soc family level fixups
dts: add support for soc family level fixups

We duplicate a lot of fixup info per board which could be done at the
SoC family level.  So introduce the concept of DTS_SOC_FIXUP_FILE which
we default to arch/<ARCH>/soc/<SOC_FAMILY>/<SOC_SERIES>/dts.fixup.

Signed-off-by: Kumar Gala <a5e5248af4cd4f0ed8c515f61d40a6e2db46a66e@linaro.org>

Vudentz/zephyr,kraj/zephyr,mbolivar/zephyr,galak/zephyr,punitvara/zephyr,kraj/zephyr,mbolivar/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,kraj/zephyr,zephyriot/zephyr,galak/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,nashif/zephyr,kraj/zephyr,explora26/zephyr,punitvara/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,ldts/zephyr,punitvara/zephyr,explora26/zephyr,nashif/zephyr,ldts/zephyr,zephyriot/zephyr,ldts/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,Vudentz/zephyr,mbolivar/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,galak/zephyr,finikorg/zephyr,zephyriot/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,zephyriot/zephyr,mbolivar/zephyr,galak/zephyr,zephyriot/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,kraj/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,finikorg/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,mbolivar/zephyr