[SCSI] bfa: add debugfs support

- Add debugfs support to obtain firmware trace, driver trace
  and read/write to registers.

- debugfs hierarchy:
  /sys/kernel/debug/bfa/host#
   where the host number corresponds to the one under /sys/class/scsi_host/host#

- Following are the new debugfs entries added:
  drvtrc: collect current driver trace
  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.

Signed-off-by: Jing Huang <huangj@brocade.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>