ASoC: meson: aiu: add support for the Meson8 and Meson8b SoC families

The AIU audio controller on the Meson8 and Meson8b SoC families is
compatible with the one found in the later GXBB family. Add compatible
strings for these two older SoC families so the driver can be loaded for
them.

Instead of using the I2S divider from the AIU_CLK_CTRL_MORE register we
need to use the I2S divider from the AIU_CLK_CTRL register. This older
register is less flexible because it only supports four divider settings
(1, 2, 4, 8) compared to the AIU_CLK_CTRL_MORE register (which supports
dividers in the range 0..64).

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20200220205711.77953-4-martin.blumenstingl@googlemail.com
Signed-off-by: Mark Brown <broonie@kernel.org>