net/mlx4_core: Implement pci_resume callback

Move resume related activities to a new pci_resume function instead of
performing them in mlx4_pci_slot_reset.  This change is needed to avoid
a hotplug during EEH recovery due to commit f2da4ccf ("powerpc/eeh:
More relaxed hotplug criterion").

Fixes: 2ba5fbd6 ('net/mlx4_core: Handle AER flow properly')
Signed-off-by: Daniel Jurgens <danielj@mellanox.com>
Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>