drm/armada: Construct a temporary crtc state for plane checks

drm/armada: Construct a temporary crtc state for plane checks

As armada isn't an atomic driver trying to pass a non-populated
crtc->state to drm_atomic_helper_check_plane_state() will end in tears.
Construct a temporary crtc state a la drm_plane_helper_check_update()
and pass that instead. For now we just really need crtc_state->enable
to be there.

Cc: Dave Airlie <airlied@redhat.com>
Cc: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180123170857.13818-3-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Dave Airlie <airlied@redhat.com>