IB/core: Add per port immutable struct to ib_device

As of commit 5eb620c8 "IB/core: Add helpers for uncached GID and P_Key
searches"; pkey_tbl_len and gid_tbl_len are immutable data which are stored in
the ib_device.

The per port core capability flags to be added later are also immutable data to
be stored in the ib_device object.

In preparation for this create a structure for per port immutable data and
place the pkey and gid table lengths within this structure.

"get_port_immutable" is added as a mandatory device function to allow the
drivers to fill in this data.

Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>