drm/amd/display: interface to check if timing can be seamless

[Why]
Need to figure out whether a timing we want to commit matches
something that GOP already programmed, in which case
we can decide to some optimizations

[How]
1. Add way to check for DIG FE
2. Add way to check for matching OTG timing
3. Add way to check for matching pixel clock (if possible)
    - Currently only support DP for pixel clock, since it is easy to calc

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