drm/meson: Add G12A Video Clock setup

While switching to the Common Clock Framework is still Work In Progress,
this patch adds the corresponding G12A HDMI PLL setup to be on-par
with the other SoCs support.

The G12A has only a single tweak about the high frequency setup,
where the HDMI PLL needs a specific setup to handle correctly the
5.94GHz DCO frequency.

Apart that, it handls ecorrectly all the other HDMI frequencies
and can achieve even better DMT clock frequency precision with
the larger fractional dividier width.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Tested-by: Jerome Brunet <jbrunet@baylibre.com>
Reviewed-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190325141824.21259-10-narmstrong@baylibre.com