drm/amd/display: Add concept of analog encoders (v2)

drm/amd/display: Add concept of analog encoders (v2)

Add a num_analog_stream_encoders field to indicate how many
analog stream encoders are present. When analog stream encoders
are present, create them.

Additionally, add an analog_engine field to link encoders and
search for supported analog encoders in the BIOS for each link.
When connecting an RGB signal, search for analog stream encoders.

The actual DCE analog link and stream encoder is going to be
added in a subsequent commit.

v2:
Add check to see if an analog engine is really supported.

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>