staging/rdma/hfi1: Adding support for hfi counters via sysfs

It enables access to counters in
/sys/class/infiniband/hfi1_0/ports/1/counters
by providing infrastructure when PMA queries occur. Counters symbol_error
and VL15_dropped are not supported in OPA, therefore, 0 will always be
returned. In addition, two common routines (pma_get_opa_port_dctrs,
pma_get_opa_port_ectrs) were created to query counters to avoid code
duplication.

Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Sebastian Sanchez <sebastian.sanchez@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>