drm/amd/display: Remove pixle rate limit for subvp

Subvp bugs related to 8K60 have been fixed, so remove the limit that
blocks 8K60 timings from enabling SubVP.

Reviewed-by: Nevenko Stupar <nevenko.stupar@amd.com>
Reviewed-by: Chaitanya Dhere <chaitanya.dhere@amd.com>
Acked-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alvin Lee <alvin.lee2@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>