toshiba_acpi: Add support for USB Sleep and Music

Newer Toshiba laptops now come with a feature called USB Sleep and
Music, where the laptop speakers remain powered and the line-in jack
is used to connect an external device to use the laptop speakers when
the computer is asleep or turned off.

This patchs adds support to such feature, by creating a sysfs entry
named "usb_sleep_music", accepting only two values, 0 to disable and
1 to enable.

Signed-off-by: Azael Avalos <coproscefalo@gmail.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>