IB/core, cma: Nice log-friendly string helpers

Some of us keep revisiting the code to decode enumerations that
appear in out logs. Let's borrow the nice logging helpers that
exists in xprtrdma and rds for CMA events, IB events and WC statuses.

Reviewd-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>