rdma/cxgb4: Fixes cxgb4 probe failure in VM when PF is exposed through PCI Passthrough

Change logic which determines our Physical Function at PCI Probe time.
Now we read the PL_WHOAMI register and get the Physical Function.

Pass Physical Function to Upper Layer Drivers in lld_info structure in the
new field "pf" added to lld_info.  This is useful for the cases where the
PF, say PF4, is attached to a Virtual Machine via some form of "PCI
Pass Through" technology and the PCI Function shows up as PF0 in the VM.

Based on original work by Casey Leedom <leedom@chelsio.com>

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