drm/amd/display: Recalculate SubVP Phantom VBlank End in dml21

drm/amd/display: Recalculate SubVP Phantom VBlank End in dml21

[WHY]
The phantom stream timing is copied from the main stream as most
parameters are identical, however some need to be recalculated.
Currently VBlank End is not recalculated and copied from the main
incorrectly.

[HOW]
Recalculate VBlank End for phantom stream timing.

Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Signed-off-by: Dillon Varone <dillon.varone@amd.com>
Signed-off-by: Wayne Lin <wayne.lin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>