drm/amd/display: add debug option for z9 disable interface

drm/amd/display: add debug option for z9 disable interface

[Why]
To help triage issues and coordinate driver/bios release dependency

[How]
Only enable the new Z9 interface when debug option is set, otherwise
treat Z10 only support case as Zstate disallowed.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Eric Yang <Eric.Yang2@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>