ARM: dts: dra7-evm: Audio support

The board uses tlv320aic3106 codec connected to McASP3. The master clock
for the codec and McASP3 is coming from ATL2.
McASP3 is the master on the I2S bus.

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