net/mlx5: Move SRQ functions to RDMA part

There is no need to keep SRQ which is RDMA object in mlx5_core.
In this patch, we partially move the execution code, while next patches
will move table initialization/release logic too.

Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>