drm/meson: dw-hdmi: add bandgap setting for g12

When no mode is set, the utility pin appears to be grounded. No signal
is getting through.

This is problematic because ARC and eARC use this line and may do so even
if no display mode is set.

This change enable the bandgap setting on g12 chip, which fix the problem
with the utility pin. This is done by restoring init values on PHY init and
disable.

Fixes: 3b7c1237

 ("drm/meson: Add G12A support for the DW-HDMI Glue")
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20240426160256.3089978-3-jbrunet@baylibre.com
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240426160256.3089978-3-jbrunet@baylibre.com