drm/amd/display: fix CTS 4.2.2.8

drm/amd/display: fix CTS 4.2.2.8

[Why]
1-Test equipment does not reset test automation flag after completing
current test causing the next test to fail.
2.When test request is empty, we shouldn't ack the test.

[How]
1-Driver should always clear test equipment automation test request
when request is completed.
2-Driver should clear test equipement test automation if driver does
not complete the request.

Signed-off-by: abdoulaye berthe <abdoulaye.berthe@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>