net/mlx4_core: Refactor mlx4_cmd_init and mlx4_cmd_cleanup

Refactoring mlx4_cmd_init and mlx4_cmd_cleanup such that partial init
and cleanup are possible. After this refactoring, calling mlx4_cmd_init
several times is safe.

This is necessary in the VF init flow when mlx4_init_hca returns -EACCESS,
we need to issue cleanup and re-attempt to call it with the slave flag.

Signed-off-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>