net/mlx4_core: Avoid repeated calls to pci enable/disable

Maintain the PCI status and provide wrappers for enabling and disabling
the PCI device.  Performing the actions more than once without doing
its opposite results in warning logs.

This occurred when EEH hotplugged the device causing a warning for
disabling an already disabled device.

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>