x86: dfi-bt700: Add xHCI USB support

Change from EHCI to xHCI on the DFI BayTrail SoM.

The xHCI USB hub is connected to an GPIO on the DFI BayTrail SoM. For
correct operation, it needs to get reset upon power-up. Otherwise it
may happen that the hub is not detected after a software reboot. This
patch also configures this GPIO in the dts for correct operation.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/board/dfi/dfi-bt700/Kconfig b/board/dfi/dfi-bt700/Kconfig
index 3f0acb3..fca8b53 100644
--- a/board/dfi/dfi-bt700/Kconfig
+++ b/board/dfi/dfi-bt700/Kconfig
@@ -21,6 +21,7 @@
 	select X86_RESET_VECTOR if !EFI_STUB
 	select INTEL_BAYTRAIL
 	select BOARD_ROMSIZE_KB_8192
+	select BOARD_LATE_INIT
 
 config PCIE_ECAM_BASE
 	default 0xe0000000