sony-laptop: Add support for recent Vaios Fn keys (C series for now)

Recent Vaios (C, AR, N, FE) need some special initialization
sequence to enable Fn keys interrupts through the Embedded
Controller. Moreover Fn keys have to be decoded internally
using ACPI methods to get the key code.
Thus a new DMI table to add SNC init time callbacks and new
mappings for model-specific key code to generic sony-laptop
code have been added.

Signed-off-by: Mattia Dongili <malattia@linux.it>
Signed-off-by: Len Brown <len.brown@intel.com>