sony_acpi: Add backlight support to the sony_acpi v2
Enable the sony_acpi driver to use the backlight subsysyem for adjusting
the monitor brightness. Old way of changing the brightness will be still
available for compatibility with existing tools.
Signed-off-by: Alessandro Guido <alessandro.guido@gmail.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Mattia Dongili <malattia@linux.it> Signed-off-by: Len Brown <len.brown@intel.com>