Fallback BUTTON_SELECT to BACK

Similar to 0b607447, BUTTON_SELECT currently falls back to MENU. This has
no known use. This fallback makes many non-android gamepads act
similarly to android specific gamepads, while giving apps the
opportunity to intercept the the keypress and handle it as before.

Change-Id: Id965fa79949dc0957e188ce4bb1bf5b125776852