soc/intel/skylake: Clean up XHCI code

Don't need "skylake/include/soc/xhci.h", hence removed.

Change-Id: I35df2003f311b557b622ce1d7a1c2e832693c2fc
Signed-off-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-on: https://review.coreboot.org/18508
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/intel/skylake/xhci.c

@@ -21,7 +21,6 @@
 #include <device/pci_ids.h>
 #include <arch/io.h>
 #include <soc/ramstage.h>
-#include <soc/xhci.h>
 #include <soc/cpu.h>
 
 static struct device_operations usb_xhci_ops = {