toshiba_acpi: Add support to enable/disable USB 3

Toshiba laptops that come with USB 3 ports have a feature that lets
them disable USB 3 functionality and act as a regular USB 2 port, and
thus, saving power.

This patch adds support to that feature, by creating a sysfs entry
named "usb_three", acceptig only two parameters, 0 to disable the
USB 3 (acting as a USB 2) and 1 to enable it, however, a reboot is
needed everytime this is toggled.

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