ARM: dts: am43xx-epos-evm: Add gpio-hog for configuring the display/audio mux

GPIO2_1 is used as a mux switch between LCD and HDMI displays. This mux
affects audio routing as well since in LCD mode HDMI audio is not possible
and when HDMI is selected analog audio is not working.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>