drm/amd/display: Implement DCE analog stream encoders

drm/amd/display: Implement DCE analog stream encoders

Add analog stream encoders for DCE which will be used when
connecting an analog display through VGA or DVI-I.

Considering that all stream encoder functions currently deal
with digital streams, there is nothing for an analog stream
encoder to do, making them basically a no-op.
That being said, we still need some kind of stream encoder to
represent an analog stream, and it is beneficial to split them
from digital stream encoders in the code to make sure they
don't accidentally write any DIG* registers.

On supported chips there is currently up to 1 analog encoder,
which is DACA. There are references to DACB in some code such
as VBIOS commands and register files but it seems to be
not present on DCE 6 and newer.

Set num_analog_stream_encoder = 1 so that we can support
the analog connectors on DCE 6-10, for now.

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>