drm/amd/display: Cache streams targeting link when performing LT automation

[WHY]
Last LT automation update can cause crash by referencing current_state and
calling into dc_update_planes_and_stream which may clobber current_state.

[HOW]
Cache relevant stream pointers and iterate through them instead of relying
on the current_state.

Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Signed-off-by: Ivan Lipski <ivan.lipski@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>