drm/amd/display: cleanup of function pointer tables

[Why]
It is becoming increasingly hard to figure out which
function is called on the different DCN versions

[How]
1. Make function pointer table init in its own init.c file
2. Remove other scenarios in hwseq.c file that need to
include headers of other DCN versions. (If needed,
it should have been done via the function pointers)

Signed-off-by: Anthony Koo <Anthony.Koo@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>