drm/i915/gem: Drop lru bumping on display unpinning

Simplify the frontbuffer unpin by removing the lock requirement. The LRU
bumping was primarily to protect the GTT from being evicted and from
frontbuffers being eagerly shrunk. Now we protect frontbuffers from the
shrinker, and we avoid accidentally evicting from the GTT, so the
benefit from bumping LRU is no more, and we can save more time by not.

Reported-and-tested-by: Matti Hämäläinen <ccr@tnsp.org>
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2905


Fixes: c1793ba8 ("drm/i915: Add ww locking to pin_to_display_plane, v2.")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210119214336.1463-6-chris@chris-wilson.co.uk


(cherry picked from commit 14ca83ee)
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: <stable@vger.kernel.org> # v5.10+
Signed-off-by: Jani Nikula <jani.nikula@intel.com>