ARM: dts: dra72-evm: Add gpio hog for vin6_sel_s0 to select audio

The GPIO expander's p1 on i2c5 bus 0x26 address is used for selecting
between audio and VIN6 functionality. For VIN6 use an add on card is
needed while audio is present on the board itself.
Select the audio functionality over the VIN6 in the dts file.

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