arm64: dts: renesas: Consolidate Salvator-X(S) HDMI0 handling

Now all Salvator-X(S) SoC/board combinations have support for HDMI
sound, all HDMI0 connector and sound descriptions are identical.
Replace them by shared descriptions in salvator-common.dtsi, to reduce
duplication.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/20210303140529.3941670-1-geert+renesas@glider.be