acer-wmi: Add DMI match for mail LED on Acer TravelMate 4200 series

The TM4200 series use the same method as the TM2490 series to control the
mail LED, so add a DMI based quirk for these laptops.

Signed-off-by: Carlos Corbacho <carlos@strangeworlds.co.uk>
Signed-off-by: Len Brown <len.brown@intel.com>