RDMA/rxe: Remove pkey table

The RoCE spec requires RoCE devices to support only the default pkey.
However the rxe driver maintains a 64 enties pkey table and uses only the
first entry. Remove the pkey table and hard code a table of length one
hard wired with the default pkey. Replace all checks of the pkey_table
with a comparison to the default_pkey instead.

Link: https://lore.kernel.org/r/20200721101618.686110-1-kamalheib1@gmail.com
Signed-off-by: Kamal Heib <kamalheib1@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>