drm/amd/display: Program VTG params after programming Global Sync for DCN2

drm/amd/display: Program VTG params after programming Global Sync for DCN2

[Why]
VTG has a parameter FP2, which is defined as:
    if VSTARTUP is before VSYNC:
        FP2 = number of lines in between VSTARTUP and VSYNC
    else
        FP2 = 0
Currently, FP2 is only programmed during "program_timing". However, the
position of VSTARTUP is affected by the prefetching requirements on all pipes,
so the position might change when we do memory request control on another pipe, so we need
to make sure that FP2 stays up-to-date whenever we adjust VSTARTUP.

[How]
 - refactor VTG_CONTROL programming into a new function "set_vtg_params"
 - call it after calling "program_global_sync"
   - make sure it's called after because it relies on the cached dlg params

Signed-off-by: Joshua Aberback <joshua.aberback@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Acked-by: Jun Lei <Jun.Lei@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>