arm64: dts: add support to analog audio playback

arm64: dts: add support to analog audio playback

This patch adds support to analog audio playback.
Only tested with headphones.
TODO: more testing on earphones and speakers.

to play analog audio on headpones:
amixer cset numid=18,iface=MIXER,name='RX1 MIX1 INP1' 'RX1'
amixer cset numid=21,iface=MIXER,name='RX2 MIX1 INP1' 'RX2'
amixer cset numid=5,iface=MIXER,name='RX1 Digital Volume' 60
amixer cset numid=6,iface=MIXER,name='RX2 Digital Volume' 60
amixer cset numid=25,iface=MIXER,name='RDAC2 MUX' 'RX2'
aplay -D hw:0,0 /usr/share/sounds/alsa/*

To play audio on HDMI:
aplay -D hw:0,1 /usr/share/sounds/alsa/*

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>