hwdb: Add key mappings for Logitech 27 MHz S520 keyboard

hwdb: Add key mappings for Logitech 27 MHz S520 keyboard

The upcoming kernel enumerates Logitech 27 MHz wireless keyboards and
mice by there wireless-PID, rather then using the PID of the receiver
which is the same for all 27MHz Logitech devices.

This allows us to add per model keymappings for the special keys on these
keyboards. This commit adds such mappings for the S520 keyboard
(modelnumber Y-RBA97).