cxgb4: support running the driver on PCI functions besides 0

Add support for running the driver on any PCI function.  Mostly this
entails replacing a constant 0 in a number of calls with the variable
function number.

Signed-off-by: Dimitris Michailidis <dm@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>