cxgb4: add adapter hotplug support for ULDs

Upon adapter hotplug, cxgb4 registers ULD devices for all the ULDs that
are already loaded, ensuring that ULD's can enumerate the hotplugged
adapter without reloading the ULD.

Signed-off-by: Potnuri Bharat Teja <bharat@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>