drm/i915: Populate possible_crtcs for primary/cursor planes

We're currently not providing the possible_crtcs mask to
drm_universal_plane_init() for primary/cursor planes. While that does
work on account of drm_crtc_init_with_planes() filling those up
for us, it's inconsisten with what we're doing for sprite planes.

Let's just always pass the possible_crtcs bitmask to
drm_universal_plane_init(). This does assume that crtc->index
== pipe. But we're already making that assumption elsewhere so
it doesn't seem like a very big sin here.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181005125817.22576-3-ville.syrjala@linux.intel.com