drm/amd/display: Interface for LTTPR interop

[WHY]
The logic to toggle LTTPR transparent/non-transparent requires 2 flags
provided by BIOS

[HOW]
Repurpose the interface to get dce caps so both LTTPR querying functions
can use them.

Signed-off-by: Wesley Chalmers <Wesley.Chalmers@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Anson Jacob <Anson.Jacob@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>