drm/amd/display: Fix vupdate and vline position calculation

[how]
Large deltas for periodic interrupts could result in the interrupt not
being programmed properly and thus not firing.

[why]
Add proper wrap-around support for calculating VUPDATE and VLINE
positions.

Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Aric Cyr <aric.cyr@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>