The muxing can actually happen on both channels on some SoCs, so it makes
more sense to just move it out of the sun4i_tcon1_mode_set function and
create a separate function that needs to be called by the encoders.

Let's do that and convert the existing drivers.
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>