bna: Add debugfs interface.

Change details:
	- Add debugfs support to obtain firmware trace, saved firmware trace on
	  an IOC crash, driver info and read/write to registers.

	- debugfs hierarchy:
	  bna/pci_dev:<pci_name>
	  where the pci_name corresponds to the one under /sys/bus/pci/drivers/bna

	- Following are the new debugfs entries added:
	  fwtrc: collect current firmware trace.
	  fwsave: collect last saved fw trace as a result of firmware crash.
	  regwr: write one word to chip register
	  regrd: read one or more words from chip register.
	  drvinfo: collect the driver information.

Signed-off-by: Krishna Gudipati <kgudipat@brocade.com>
Signed-off-by: David S. Miller <davem@davemloft.net>