net/mlx5: Split the load/unload flow into hardware and software flows

Gather all software context creating/destroying in one function and call
it once in the first load and in the last unload.
load/unload functions will now receive indication if we need to
create/destroy the software contexts.
In internal/pci error do the unload/load flows without releasing the
software objects.
In this way we perserve the sw core state and it help us restoring old
driver state after PCI error/shutdown.

Signed-off-by: Mohamad Haj Yahia <mohamad@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>