toshiba_acpi: Add support for USB Sleep and Charge function

Newer Toshiba models now come with a feature called Sleep and Charge,
where the computer USB ports remain powered when the computer is
asleep or turned off.

This patch adds support to such feature, creating a sysfs entry
called "usb_sleep_charge" to set the desired charging mode or to
disable it.

The sysfs entry accepts three parameters, 0, 1 and 2, beign disabled,
alternate and auto respectively.

The auto mode stands for USB conformant devices (which most are), and
the alternate mode stands for those non USB conformant devices that
require more power.

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