drm/amd/display: Ignore k1/k2 values for virtual signal

[Why and How]
We are hitting k1/k2 assert when we are using a virtual signal in the
test; as a result, we are failing some automated tests with a false
positive. This commit addresses this issue by ignoring the assert
condition if we use SIGNAL_TYPE_VIRTUAL.

Reviewed-by: Aurabindo Pillai <Aurabindo.Pillai@amd.com>
Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>