drm/i915: Clean up cursor junk from intel_crtc

drm/i915: Clean up cursor junk from intel_crtc

Move cursor_base, cursor_cntl, and cursor_size from intel_crtc
into intel_plane so that we don't need the crtc for cursor stuff
so much.

Also entirely nuke cursor_addr which IMO doesn't provide any benefit
since it's not actually used by the cursor code itself. I'm not 100%
sure what the SKL+ DDB is code is after by looking at cursor_addr so
I just make it do its checks unconditionally. If that's not correct
then we should likely replace it with somehting like
plane_state->visible.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170327185546.2977-5-ville.syrjala@linux.intel.com
Reviewed-by: Imre Deak <imre.deak@intel.com>