mlx5: Move pci device handling from mlx5_ib to mlx5_core

In preparation for a new mlx5 device which is VPI (i.e., ports can be
either IB or ETH), move the pci device functionality from mlx5_ib
to mlx5_core.

This involves the following changes:
1. Move mlx5_core_dev struct out of mlx5_ib_dev. mlx5_core_dev
   is now an independent structure maintained by mlx5_core.
   mlx5_ib_dev now has a pointer to that struct.
   This requires changing a lot of places where the core_dev
   struct was accessed via mlx5_ib_dev (now, this needs to
   be a pointer dereference).
2. All PCI initializations are now done in mlx5_core. Thus,
   it is now mlx5_core which does pci_register_device (and not
   mlx5_ib, as was previously).
3. mlx5_ib now registers itself with mlx5_core as an "interface"
   driver. This is very similar to the mechanism employed for
   the mlx4 (ConnectX) driver. Once the HCA is initialized
   (by mlx5_core), it invokes the interface drivers to do
   their initializations.
4. There is a new event handler which the core registers:
   mlx5_core_event(). This event handler invokes the
   event handlers registered by the interfaces.

Based on a patch by Eli Cohen <eli@mellanox.com>

Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Eli Cohen <eli@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>