nvramcui: Add USB support

Enable the USB during the initialization of nvramcui. Without it
the USB keyboards don't work, which makes this payload pointless
on the systems where a PS/2 keyboard port isn't available.

Based on https://review.coreboot.org/#/c/17507/

Change-Id: I04697c5f582b41e6f6ffe98955bf59f4fe57f66e
Signed-off-by: Nicola Corna <nicola@corna.info>
Reviewed-on: https://review.coreboot.org/18765
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Rudolph <siro@das-labor.org>

payloads/nvramcui/nvramcui.c

@@ -176,6 +176,10 @@ int main(void)
 	int ch, done;
 	int i;
 
+#if IS_ENABLED(CONFIG_LP_USB)
+	usb_initialize();
+#endif
+
 	/* coreboot data structures */
 	lib_get_sysinfo();