drm/amd/display: Add a sanity check for DSC already enabled/disabled

[why]
If acquire/release DSC resource sequence is affected by a regression,
it can happen that the already-in-use DSC HW block is being wrongly
re-used for a different pipe. The reverse is also possible, i.e.
already-disabled DSC HW block could be disabled from other context.

[how]
Read back the enable state of DSC HW and report an error if duplicate
enable or disable was attempted.

Signed-off-by: Nikola Cornij <nikola.cornij@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>