drm/amd/display: change zstate allow msg condition

[Why]
PMFW message which previously thought to only control Z9 controls both
Z9 and Z10. Also HW design team requested that Z9 must only be supported
on eDP due to content protection interop.

[How]
Change zstate support condition to match updated policy

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>