sony-laptop: VGN-A317M hotkey support

This laptop has 5 SPIC managed buttons above the keyboard:
sound + and - as well as brightness, zoom and S1.
Possibly the entire VGN-A serie behaves the same.

Signed-off-by: Harald Jenny <harald@a-little-linux-box.at>
Signed-off-by: Mattia Dongili <malattia@linux.it>
Signed-off-by: Len Brown <len.brown@intel.com>