soc/intel/cannonlake: Limit xDCI feature when VBOOT is enabled

Use the common xDCI function to check if the controller is allowed
in the current mode before enabling it.  Otherwise, disable the
PCI device if it has been enabled in devicetree.

To make the SOC behavior consistent the XdciEnable config option
is removed in favor of direct control by devicetree.cb.

Change-Id: I34e7d750d3f75757a68977ae8d92bfbee1a10af1
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://review.coreboot.org/25366
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Lijian Zhao <lijian.zhao@intel.com>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/intel/cannonlake/Kconfig

@@ -70,6 +70,7 @@ config CPU_SPECIFIC_OPTIONS
 	select SOC_INTEL_COMMON_BLOCK_SPI
 	select SOC_INTEL_COMMON_BLOCK_TIMER
 	select SOC_INTEL_COMMON_BLOCK_UART
+	select SOC_INTEL_COMMON_BLOCK_XDCI
 	select SOC_INTEL_COMMON_NHLT
 	select SOC_INTEL_COMMON_RESET
 	select SSE2