drm/amdgpu/display: Only set vblank_disable_immediate when PSR is not enabled

drm/amdgpu/display: Only set vblank_disable_immediate when PSR is not enabled

[ Upstream commit 70897848730470cc477d5d89e6222c0f6a9ac173 ]

[Why]
PSR currently relies on the kernel's delayed vblank on/off mechanism
as an implicit bufferring mechanism to prevent excessive entry/exit.

Without this delay the user experience is impacted since it can take
a few frames to enter/exit.

[How]
Only allow vblank disable immediate for DC when psr is not supported.

Leave a TODO indicating that this support should be extended in the
future to delay independent of the vblank interrupt.

Fixes: 92020e81ddbeac ("drm/amdgpu/display: set vblank_disable_immediate for DC")
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>