net/mlx5: Fix crash upon suspend/resume

Currently a Linux system with the mlx5 NIC always crashes upon
hibernation - suspend/resume.

Add basic callbacks so the NIC could be suspended and resumed.

Fixes: 9603b61d

 ("mlx5: Move pci device handling from mlx5_ib to mlx5_core")
Tested-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Mark Bloch <markb@mellanox.com>
Reviewed-by: Moshe Shemesh <moshe@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>