dt-bindings: clock: meson8b: add the audio clocks

The audio controllers on Meson8, Meson8b and Meson8m2 use similar
(potentially the same) audio clocks as GXBB, GXL and GXM. Add the
CLKID_CTS_AMCLK, CLKID_CTS_MCLK_I958 and CLKID_CTS_I958 clock IDs so
they can be used for the audio controllers.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>