drm/i915: Clean up intel_{pre,post}_plane_update()

Change the calling convention to just pass the state+crtc and
switch to intel_ types throughout.

We'll also do a quick s/if (old_primary_state)/if (new_primary_state)/
so that we'll be able to eliminate old_primary_state later. This
is fine since we always have either both old and new state or neither.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191127190556.1574-5-ville.syrjala@linux.intel.com
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>