arm64: dts: renesas: salvator-common: use audio-graph-card for Sound

Current Sound is using simple-audio-card which can't support HDMI.
To use HDMI sound, we need to use audio-graph-card.
But, one note is that r8a7795 has 2 HDMI ports, but r8a7796 has 1.
Because of this mismatch, supporting HDMI on salvator-common is
impossible.
Thus, this patch exchange sound card to audio-graph-card and keep
supporting ak4613 as 1st sound node.
r8a7795/r8a7796 salvator-x{s} need to add HDMI sound individually.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: Nguyen Viet Dung <nv-dung@jinso.co.jp>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>