ALSA: preliminary support for Toshiba SB-0500

The Toshiba Multimedia Center SB-0500 is a rebranded version of the
Creative Technology SB Live! 24-bit External: it shares the same chipset
and only has minor cosmetic differences. Remote controller works with
alsa_usb module, basic audio is there and mixer controls are mostly
untested.

Signed-off-by: Andrea Borgia <andrea@borgia.bo.it>
Signed-off-by: Takashi Iwai <tiwai@suse.de>