Use SoC instead of platform.

Change terminology and use SoC instead of platform. An SoC provides
features and default configurations available with an SoC. A board
implements the SoC and adds more features and IP block specific to the
board to extend the SoC functionality such as sensors and debugging
features.

Change-Id: I15e8d78a6d4ecd5cfb3bc25ced9ba77e5ea1122f
Signed-off-by: Anas Nashif <anas.nashif@intel.com>

arch/arm/Kbuild

@@ -3,4 +3,4 @@ subdir-ccflags-y +=-I$(srctree)/drivers
 subdir-asflags-y := ${subdir-ccflags-y}
 
 obj-y += core/
-obj-y += platforms/$(PLATFORM_NAME)/
+obj-y += soc/$(SOC_NAME)/