This commit adds a hotkey to switch between "gamepad" mode (mouse and keyboard
disabled) and "desktop" mode (gamepad disabled) by holding down the options
button (mapped here as the start button). This mirrors the behavior of the
official Steam client.

This also adds and uses a function for generating haptic pulses, as Steam also
does when engaging this hotkey.
Signed-off-by: Vicki Pfau <vi@endrift.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>