drm/amd/display: Optimizations for DML math

[why]
Conditionals in the DML basic math functions significantly impact mode
enumeration.

[how]
Remove conditionals for floor/ceil operations which are used frequently
in DML and add an assertion for invalid callers using zero granuality.
Fix existing callers that rely on 0 granularity.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Nevenko Stupar <Nevenko.Stupar@amd.com>
Acked-by: Pavle Kotarac <Pavle.Kotarac@amd.com>
Signed-off-by: Aric Cyr <aric.cyr@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>