arm64: dts: rockchip: enable HDMI audio on Rock 5 ITX

arm64: dts: rockchip: enable HDMI audio on Rock 5 ITX

The Rock 5 ITX only needs enablement for 2 nodes in order to send audio
on HDMI1, the connector closer to the 12V barrel jack and farther from
S/PDIF.  It is sufficient to declare the audio injection as okay, and
to activate I2S6.

Note that for the other HDMI output it is not that trivial, as the video
data there originates from the SoC's DisplayPort output DP1 and is only
converted to HDMI in U7 (an RA620).

Signed-off-by: Torsten Duwe <duwe@lst.de>
[fixed commit subject prefixes]
Link: https://patch.msgid.link/20251110181153.CC62B6732A@verein.lst.de
Signed-off-by: Heiko Stuebner <heiko@sntech.de>