IB/core: Expose RSS related capabilities

Expose RSS related capabilities, it includes both direct ones (i.e.
struct ib_rss_caps) and max_wq_type_rq which may be used in both
RSS and non RSS flows.

Specifically,
supported_qpts:
- QP types that support RSS on the device.

max_rwq_indirection_tables:
- Max number of receive work queue indirection tables that
  could be opened on the device.

max_rwq_indirection_table_size:
- Max size of a receive work queue indirection table.

max_wq_type_rq:
- Max number of work queues of receive type that
  could be opened on the device.

Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>