mb/google/skywalker: Set up USB host in ramstage

Add USB host function support.

BUG=b:379008996
BRANCH=none
TEST=boot to kernel successfully from USB drive

Signed-off-by: Liu Liu <ot_liu.liu@mediatek.corp-partner.google.com>
Change-Id: I3f77d116033338f979d14ce34ddf03e00d024e5d
Reviewed-on: https://review.coreboot.org/c/coreboot/+/87022
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yidi Lin <yidilin@google.com>

src/mainboard/google/skywalker/mainboard.c

@@ -1,10 +1,11 @@
 /* SPDX-License-Identifier: GPL-2.0-only OR MIT */
 
 #include <device/device.h>
+#include <soc/usb.h>
 
 static void mainboard_init(struct device *dev)
 {
-	/* TODO: add mainboard init */
+	setup_usb_host();
 }
 
 static void mainboard_enable(struct device *dev)