drm/amd/display: Explicitly disable triplebuffer flips

[Why]
This is enabled by default on Renoir but there's userspace/API support
to actually make use of this.

Since we're not passing this down through surface updates, let's
explicitly disable this for now.

This fixes "dcn20_program_front_end_for_ctx" warnings associated with
incorrect/unexpected programming sequences performed while this is
enabled.

[How]
Disable it at the topmost level in DM in case anyone tries to flip this
to enabled for any of the other ASICs like Navi10/14.
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Hersen Wu <hersenxs.wu@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -3022,6 +3022,9 @@ static int amdgpu_dm_initialize_drm_device(struct amdgpu_device *adev)
 	if (adev->asic_type != CHIP_CARRIZO && adev->asic_type != CHIP_STONEY)
 		dm->dc->debug.disable_stutter = amdgpu_pp_feature_mask & PP_STUTTER_MODE ? false : true;
 
+	/* No userspace support. */
+	dm->dc->debug.disable_tri_buf = true;
+
 	return 0;
 fail:
 	kfree(aencoder);