drm/i915: Handle disabling planes better, v2.

Read out the initial state, and add a quirk to force add all planes
to crtc_state->plane_mask during initial commit. This will disable
all planes during the initial modeset.

The initial plane quirk is temporary, and will go away when hardware
readout is fully atomic, and the watermark updates in intel_sprite.c
are removed.

Changes since v1:
- Unset state->visible on !primary planes.
- Do not rely on the plane->crtc pointer in intel_atomic_plane,
  instead assume planes are invisible until modeset.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Tested-by(IVB): Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>