soc/intel/cannonlake: Add CONFIG_SMM_RESERVED_SIZE config

This patch ensures to make SMM_RESERVED_SIZE for cannonlake platform
else smm_subregion() returns 0 size.

Change-Id: I6a95a244bbcf40d672fd11d1c62e01224b2554f2
Signed-off-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-on: https://review.coreboot.org/26216
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Rizwan Qureshi <rizwan.qureshi@intel.com>

src/soc/intel/cannonlake/Kconfig

@@ -177,6 +177,10 @@ config SMM_TSEG_SIZE
 	hex
 	default 0x800000
 
+config SMM_RESERVED_SIZE
+	hex
+	default 0x200000
+
 config PCR_BASE_ADDRESS
 	hex
 	default 0xfd000000