drm/amd/display: Implement DCE analog link encoders (v2)

drm/amd/display: Implement DCE analog link encoders (v2)

We support two kinds of analog connections:

1. DVI-I, which allows both digital and analog signals:
The DC code base only allows 1 encoder per connector, and the
preferred engine type is still going to be digital. So, for DVI-I
to work, we need to make sure the pre-existing link encoder can
also work with analog signals.

1. VGA, which only supports analog signals:
For VGA, we need to create a link encoder that only works with the
DAC without perturbing any digital transmitter functionality.
Since dce110_link_encoder already supports analog DVI-I,
just reuse that code for VGA as well.

v2:
Reduce code churn by reusing same link encoder for VGA and DVI-I.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>