drm/amd/display: Fill in vrefresh and min_vblank_time for dce8/dce10

PPLib is now calling into DC to get vrefresh and min_vblank_time, but
since full bandwidth calcs are missing for those generations, the pplib
structures were never being filled. This change fills the currently
required fields to prevent screen corruption.

Signed-off-by: Jordan Lazare <Jordan.Lazare@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Reviewed-by: Jordan Lazare <Jordan.Lazare@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>