Currently the rxe driver uses red-black trees to add indices to the rxe
object pools. Linux xarrays provide a better way to implement the same
functionality for indices. This patch replaces red-black trees by xarrays
for pool objects. Since xarrays already have a spinlock use that in place
of the pool rwlock. Make sure that all changes in the xarray(index) and
kref(ref counnt) occur atomically.

Link: https://lore.kernel.org/r/20220304000808.225811-9-rpearsonhpe@gmail.comSigned-off-by: NBob Pearson <rpearsonhpe@gmail.com>
Signed-off-by: NJason Gunthorpe <jgg@nvidia.com>