IB/cma: Helper functions to access port space IDRs

Add helper functions to access the IDRs by port-space and port number.

Pass around the port-space enum in cma.c instead of using pointers to
port-space IDRs.

Signed-off-by: Haggai Eran <haggaie@mellanox.com>
Signed-off-by: Yotam Kenneth <yotamke@mellanox.com>
Signed-off-by: Shachar Raindel <raindel@mellanox.com>
Signed-off-by: Guy Shapiro <guysh@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>