drm/amd/display: Add DMUB service function check if hw initialized

[Why]
We want to avoid reprogramming the cache window when possible.

We don't need to worry about it for S3 but we *do* need to worry about
it for S4 resume.

DM can check whether hardware should be reinitialized or store software
state when going to S4 to know whether we need to reprogram hardware.

[How]
Add helpers to the DMUB service to check hardware initialization state.

DM will hook it up later.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@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>