drm/amd/display: Reset link encoder assignments for GPU reset

[Why]
A warning appears in the log on GPU reset for
link_enc_cfg_link_encs_assign for the following condition:

ASSERT(state->res_ctx.link_enc_cfg_ctx.link_enc_assignments[i].valid == false);

This is not expected behavior and may result in link encoders being
incorrectly assigned.

[How]
The dc->current_state is backed up into dm->cached_dc_state before
we commit 0 streams.

DC will clear link encoder assignments on the real state but the
changes won't propagate over to the copy we made before the
0 streams commit.

DC expects that link encoder assignments are *not* valid
when committing a state, so as a workaround it needs to be cleared
before passing it back into DC.

Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -2561,6 +2561,20 @@ static int dm_resume(void *handle)
 	if (amdgpu_in_reset(adev)) {
 		dc_state = dm->cached_dc_state;
 
+		/*
+		 * The dc->current_state is backed up into dm->cached_dc_state
+		 * before we commit 0 streams.
+		 *
+		 * DC will clear link encoder assignments on the real state
+		 * but the changes won't propagate over to the copy we made
+		 * before the 0 streams commit.
+		 *
+		 * DC expects that link encoder assignments are *not* valid
+		 * when committing a state, so as a workaround it needs to be
+		 * cleared here.
+		 */
+		link_enc_cfg_init(dm->dc, dc_state);
+
 		amdgpu_dm_outbox_init(adev);
 
 		r = dm_dmub_hw_init(adev);