soc/intel/cannonlake: Change max root port to 16

Cannonlake SOC support up to 16 PCI express root port.

BUG=CID 1381813;1381814;

Change-Id: I4df610e3fb01bd8e62be7e9c62144125f2a96c25
Signed-off-by: Lijian Zhao <lijian.zhao@intel.com>
Reviewed-on: https://review.coreboot.org/22122
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/intel/cannonlake/Kconfig

@@ -110,7 +110,7 @@ config IED_REGION_SIZE
 
 config MAX_ROOT_PORTS
 	int
-	default 24
+	default 16
 
 config SMM_TSEG_SIZE
 	hex