toshiba_acpi: Add accelerometer support

Recent Toshiba laptops now come equiped with a built in
accelerometer (TOS620A) device, but such device does not
expose the axes information, however, HCI calls 0x006d
and 0x00a6 can be used to query such info.

This patch adds support to read the axes values by
exposing them through the _position_ sysfs file.

Signed-off-by: Azael Avalos <coproscefalo@gmail.com>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>