drm/amd/display: Fix Scaling (RMX_*) for DC driver

drm/amd/display: Fix Scaling (RMX_*) for DC driver

Before:
We use drm_match_cea_mode() to get the vic for any mode we
want to set, most of the time vic will be different for the new mode.

DC uses memcmp to check if timing changed, in this case DC will
say timing changed and we endup doing a full modeset.

Current:
Now we check if !RMX_OFF and old_refresh == new_refresh if so
we copy the vic from old timing. In a case where we are currently on
a lower timing and want to change to higher mode, stream->dst will be
different and cause us to do a full modeset, which is what we want.

Signed-off-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Reviewed-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>