RDMA/efa: Expose device statistics

Expose hardware statistics through the sysfs api:
/sys/class/infiniband/efa_0/hw_counters/*.
/sys/class/infiniband/efa_0/ports/1/hw_counters/*.

Reviewed-by: Firas JahJah <firasj@amazon.com>
Reviewed-by: Yossi Leybovich <sleybo@amazon.com>
Signed-off-by: Gal Pressman <galpress@amazon.com>
Link: https://lore.kernel.org/r/20190725130353.11544-1-galpress@amazon.com


Signed-off-by: Doug Ledford <dledford@redhat.com>