soc/intel/common: Add IGD OpRegion support

Add helper function that fills OpRegion structure based on
VBT file content and some reasonable defaults.

Change-Id: I9aa8862878cc016a9a684c844ceab390734f3e84
Signed-off-by: Andrey Petrov <andrey.petrov@intel.com>
Reviewed-on: https://review.coreboot.org/14806
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/intel/common/Kconfig

@@ -72,4 +72,8 @@ config VBT_FILE
 	help
 	  The path and filename of the VBT binary.
 
+config SOC_INTEL_COMMON_GFX_OPREGION
+	bool
+	default n
+
 endif # SOC_INTEL_COMMON