soc/intel/common/systemagent: Add Kconfig guard

Looks like selecting SOC_INTEL_COMMON force-sets MMCONF_BASE_ADDR to
some value which can't be overriden outside of soc/intel/common. So
adding a non-SoC platform thats uses code from soc/intel/common is not
possible.

TEST=build test on wip platform

Change-Id: Ia160444e8ac7cac55153f659f4d98f4f77f0d467
Signed-off-by: Andrey Petrov <anpetrov@fb.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/38639
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: David Guckian

src/soc/intel/common/block/systemagent/Kconfig

@@ -3,6 +3,8 @@ config SOC_INTEL_COMMON_BLOCK_SA
 	help
 	  Intel Processor common System Agent support
 
+if SOC_INTEL_COMMON_BLOCK_SA
+
 config MMCONF_BASE_ADDRESS
 	hex
 	default 0xe0000000
@@ -36,3 +38,5 @@ config SA_ENABLE_DPR
 	default n
 	help
 	  This option allows you to add the DMA Protected Range (DPR).
+
+endif

src/soc/intel/denverton_ns/Kconfig

@@ -54,6 +54,10 @@ config CPU_SPECIFIC_OPTIONS
 	select UDK_2015_BINDING
 	select CPU_INTEL_FIRMWARE_INTERFACE_TABLE
 
+config MMCONF_BASE_ADDRESS
+	hex
+	default 0xe0000000
+
 config FSP_T_ADDR
 	hex "Intel FSP-T (temp ram init) binary location"
 	depends on ADD_FSP_BINARIES && FSP_CAR