staging/fwserial: Factor unstable stats/debug/status info to debugfs

Add the following file hierarchy to debugfs:

  <debugfs>-+
            +- firewire_serial -+- <unit> -+- peers
                                |          +- stats
                                |
                                +- <unit> -+- peers
                                           +- stats

The 'peers' file (read-only) contains status and configuration
info for attached peers for the given fwserial unit.

The 'stats' file (read-only) contains statistics and data profiling
information for each tty port for the given fwserial unit.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>