drm/i915/gen9+: Program watermarks as a separate step during evasion, v3.

The watermark updates for SKL style watermarks are no longer done
in the plane callbacks, but are now called in a separate watermark
update function that's called during the same vblank evasion,
before the plane updates.

This also gets rid of the global skl_results, which was required for
keeping track of the current atomic commit.

Changes since v1:
- Move line unwrap to correct patch. (Lyude)
- Make sure we don't regress ILK watermarks. (Matt)
- Rephrase commit message. (Matt)
Changes since v2:
- Fix disable watermark check to use the correct way to determine single
  step watermark support.

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Lyude <cpaul@redhat.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1478609742-13603-3-git-send-email-maarten.lankhorst@linux.intel.com
[mlankhorst: Small whitespace fix in skl_initial_wm]