cxgb4: Enable SR-IOV configuration via PCI sysfs interface

Implement callback in the driver for the new PCI bus driver
interface that allows the user to enable/disable SR-IOV
virtual functions in a device via the sysfs interface.

Deprecate module parameter used to configure SRIOV

Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>