drm/radeon/atom: rework DIG modesetting on DCE3+

drm/radeon/atom: rework DIG modesetting on DCE3+

commit 8d1af57ae3c4458ed0de93ef97f388dd1b3239c7 upstream.

The ordering is important and the current drm code
wasn't cutting it for modern DIG encoders.  We need
to have information about crtc before setting up
the encoders so I've shifted the ordering a bit.
Probably we'll need a full rework akin to danvet's
recent intel patchs.  This patch fixes numerous
issues with DP bridge chips and makes link training
much more reliable.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
[bwh: Backported to 3.2: drop DCE6 cases]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>