When USB keyboard active, don't send keyboard commands to ps2 port.

Route keyboard commands to a USB handler when USB keyboard is active.

Add a GETID handler for USB keyboards.
diff --git a/src/usb-hid.h b/src/usb-hid.h
index 1c75560..6af4da2 100644
--- a/src/usb-hid.h
+++ b/src/usb-hid.h
@@ -7,7 +7,9 @@
 int usb_keyboard_init(struct usb_pipe *pipe
                       , struct usb_interface_descriptor *iface, int imax);
 void usb_keyboard_setup(void);
+inline int usb_kbd_active(void);
 void usb_check_key(void);
+inline int usb_kbd_command(int command, u8 *param);