Notably when freeing a batchbuffer, we often end up freeing many of the
buffers it points at as well.  Avoiding repeated calls brings us a 9% CPU
win for cairo-gl.

[ # ]  backend                         test   min(s) median(s) stddev. count
before:
[  0]       gl            firefox-talos-gfx   58.941   58.966   0.75%    3/3
after:
[  0]       gl            firefox-talos-gfx   54.186   54.195   0.49%    3/3

If the target we're asking about hasn't ever been used as a relocation
target, then it obviously hasn't been used as a target by the batch's reloc
tree.  This is the common case for good GL programming where you only map
fresh buffers, and gives us a 5% win in cairo-gl.

[ # ]  backend                         test   min(s) median(s) stddev. count
before:
[  0]       gl            firefox-talos-gfx   64.680   64.756   0.06%    3/3
after:
[  0]       gl            firefox-talos-gfx   60.816   60.970   0.29%    3/3

Use the external implementation for atomic operations across a wide
range of architectures.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

I slipped it in with the alloc_tiled changes, since we were explicitly
throwing the parameter away.  It caught some bogus released code, which
we've now fixed, so remove the asserts to keep old drivers working.

This simplifies driver code in handling object allocation, and also gives us
an opportunity to possibly cache tiled buffers if it turns out to be a win.

[anholt: This is chopped out of the execbuf2 patch, as it seems to be useful
separately and cleans up the execbuf2 changes to be more obvious]

This is done with:
Lindent *.[ch]
perl -pi -e 's|drm_intel_bo \* |drm_intel_bo *|g' *.[ch]
perl -pi -e 's|drm_intel_bufmgr \* |drm_intel_bufmgr *|g' *.[ch]
perl -pi -e 's|drm_intel_bo_gem \* |drm_intel_bo_gem *|g' *.[ch]
perl -pi -e 's|drm_intel_bufmgr_gem \* |drm_intel_bufmgr_gem *|g' *.[ch]
perl -pi -e 's|_fake \* |_fake *|g' *.[ch]
hand-editing to whack indented comments into line and other touchups.