drm/amd/display: abstract encoder related hwseq across different types

[why]
Current we have hundreds of if/else or switch statement to check
encoder type in dc_link level. The reason is because depending
on the type of encoder dc_link needs to perform similar programming
task but with different encoder interfaces. The story is to abstract
these interfaces so dc_link can just perform the programming task
without knowing the detail of which encoder it's dealing with.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>