{net, IB}/mlx5: Refactor internal SRQ API

Currently, the SRQ API uses the obsolete mlx5_*_srq_mbox_{in,out}
structs which limit the ability to pass the SRQ attributes between
net and IB parts of the driver.

This patch changes the SRQ API so as to use auto-generated structs
and provides a better way to pass attributes which will be in use by
coming features.

Signed-off-by: Artemy Kovalyov <artemyko@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>