drm/i915: Rename intel_pin_and_map_ring()

For more consistent oop-naming, we would use intel_ring_verb, so pick
intel_ring_pin() and intel_ring_unpin().

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1469432687-22756-17-git-send-email-chris@chris-wilson.co.uk
Link: http://patchwork.freedesktop.org/patch/msgid/1470174640-18242-6-git-send-email-chris@chris-wilson.co.uk