kbuild: Don't require intel/common changes for every soc

kbuild: Don't require intel/common changes for every soc

In the true spirit of separating components more strictly
and allowing to add new components to coreboot without touching
existing code, move Intel common code selection to the soc
Kconfig and out of src/soc/intel/common/Makefile.inc

Change-Id: I0a70656bb9f4550b6088e9f45e68b5106c0eb9af
Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-on: http://review.coreboot.org/10031
Tested-by: build bot (Jenkins)
Reviewed-by: Leroy P Leahy <leroy.p.leahy@intel.com>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>