drm/amd/display: Update RN/VGH active display count workaround

[WHY]
Virtual signals were previously counted as a workaround to S0i2 hang
which is fixed on Renoir. This blocks S0i3 diags testing.

[HOW]
Stop counting virtual signals as S0i2 hang is fixed on Renoir.

Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Acked-by: Bindu Ramamurthy <bindu.r@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>