drm/amd/display: Get ceiling for v_total calc

Updating certain variable blanking calculations to use ceiling function.

Reviewed-by: Chris Park <chris.park@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Acked-by: Agustin Gutierrez <agustin.gutierrez@amd.com>
Signed-off-by: Bing Guo <Bing.Guo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>