drm/i915/skl: Implement the new update_plane() for primary planes

drm/i915/skl: Implement the new update_plane() for primary planes

Skylake makes primary planes the same as sprite planes and call the
result "universal planes".

This commit emulates a primary plane with plane 0, taking the
opportunity to redefine primary and sprite registers to be identical now
that the underlying hardware is. It also makes sense as plenty of fields
have changed.

v2: Rebase on top of the vma code.

v3: Follow upstream evolution:
- Drop return values.
- Remove pipe checks since redudant and BUG instead.
- Remove tiling checks and BUG instead.
- Drop commented out DISP_MODIFY usage.

v4: s/plane/primary_plane/

v5: Misc fixes:
- Fix the fields we need to clear up
- Disable trickle feed
- Correctly use PLANE_OFFSET for the panning

v6: (Jesse)
Use pipe src size when programming plane size. This makes cloned configs
work correctly w/o the use of a panel fitter.

v7: Rebase on top of Ville's rmw elimination series

v8: Remove clearing the trickle feed bit now that we don't do a RMW (Rodrigo,
    Damien)
    Add a comment about the stride unit (Rodrigo)

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com> (v1,5,6,7)
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> (v2,3)
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>