drm/i915: Move ddb/wm programming into plane update/disable hooks on skl+

On SKL+ the plane WM/BUF_CFG registers are a proper part of each
plane's register set. That means accessing them will cancel any
pending plane update, and we would need a PLANE_SURF register write
to arm the wm/ddb change as well.

To avoid all the problems with that let's just move the wm/ddb
programming into the plane update/disable hooks. Now all plane
registers get written in one (hopefully atomic) operation.

To make that feasible we'll move the plane ddb tracking into
the crtc state. Watermarks were already tracked there.

v2: Rebase due to input CSC
v3: Split out a bunch of junk (Matt)
v4: Add skl_wm_add_affected_planes() to deal with
    cursor special case and non-zero wm register reset value
v5: Drop the unrelated for_each_intel_plane_mask() fix (Matt)
    Remove the redundant ddb memset() (Matt)

Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> #v3
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181127165900.31298-1-ville.syrjala@linux.intel.com