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/chip.h

@@ -124,7 +124,6 @@ struct soc_intel_cannonlake_config {
 	/* USB related */
 	struct usb2_port_config usb2_ports[16];
 	struct usb3_port_config usb3_ports[10];
-	uint8_t XdciEnable;
 	uint8_t SsicPortEnable;
 	/* Wake Enable Bitmap for USB2 ports */
 	uint16_t usb2_wake_enable_bitmap;