drm/amd/display: skip opp blank or unblank if test pattern enabled

[why]
DPG is used to generate both blank and test automation test pattern.
When test automation is running the requested test pattern can be
overriden by the blank or unblank call because it is using the same
hardware.

[how]
When test pattern is requested, skip blank or unblank.

Signed-off-by: Wenjing Liu <Wenjing.Liu@amd.com>
Reviewed-by: Nikola Cornij <Nikola.Cornij@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>