staging: line6: add Pod HD300 support

The Pod HD device family uses new MIDI SysEx messages and therefore
cannot reuse the existing Pod code.  Instead of hardcoding Pod HD MIDI
messages into the driver, leave MIDI up to userspace.  This driver
simply presents MIDI and pcm ALSA devices.

This device is similar to the Pod except that it has 48 kHz audio and
does not respond to Pod SysEx messages.

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>