netxen: implement generic pcie semaphore functions

Implement common function for locking/unlocking 8 hardware
semaphores used for serializing access to shared resouces
on a NIC board by different PCI functions.

As by definition, callers of these semaphore API can be
put to sleep till the semaphore is locked.

Signed-off-by: Dhananjay Phadke <dhananjay@netxen.com>
Signed-off-by: David S. Miller <davem@davemloft.net>