drm/amd/display: move panel power seq to new panel struct

[Why]
panel power sequencer is currently just sitting in hwseq but it really
it tied to internal panels

[How]
make a new panel struct to contain power sequencer code

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