IB/core: Add OPA MAD core capability flag

Add OPA MAD support flags to the core capability immutable flags.  In addition
add the rdma_cap_opa_mad helper function for core functions to use to detect
OPA MAD support.

OPA MADs share a common header with IBTA MADs but with some differences for
increased performance.

Sharing a common header with IBTA MADs allows us to share most of the MAD
processing code when dealing with OPA MADs in addition to supporting some IBTA
MADs on OPA devices.

OPA MADs differ in the following ways:

	1) MADs are variable size up to 2K
	   IBTA defined MADs remain fixed at 256 bytes
	2) OPA SMPs must carry valid PKeys
	3) OPA SMP packets are a different format

The MAD stack will use this new functionality to determine if OPA MAD
processing should occur on individual device ports.

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