RDMA/uverbs: Export XRC SRQs to user space

We require additional information to create XRC SRQs than we can
exchange using the existing create SRQ ABI.  Provide an enhanced create
ABI for extended SRQ types.

Based on patches by Jack Morgenstein <jackm@dev.mellanox.co.il>
and Roland Dreier <roland@purestorage.com>

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>