drm/i915: Introduce crtc_state->update_planes bitmask

drm/i915: Introduce crtc_state->update_planes bitmask

Keep track which planes need updating during the commit. For now
we set the bit for any plane that was or will be visible (including
icl+ nv12 slave planes). In the future I'll have need to update
invisible planes as well, for skl plane ddbs and for pre-skl pipe
gamma/csc control (which lives in the primary plane control register).

v2: Pimp the commit message to mention icl+ nv12 slave planes (Matt)

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181127163742.30215-1-ville.syrjala@linux.intel.com