platform/x86: fujitsu-laptop: Support Lifebook U7x7 hotkeys

Generate input events for hotkeys present in Fujitsu Lifebook
U727 and U757 laptops:
  - Fn+F1 (KEY_MICMUTE)
  - Fn+F5 (KEY_RFKILL)

Signed-off-by: Jan-Marek Glogowski <glogow@fbihome.de>
Reviewed-by: Jonathan Woithe <jwoithe@just42.net>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>