hwdb: keyboard: Ignore duplicate atkbd keypresses on touchpad on/off toggle

The atkbd device on the Lenovo Yoga 300-11IBR 2-in-1 sends unknown
keycodes when the touchpad is toggled on/off:

[ 1918.995562] atkbd serio0: Unknown key pressed (translated set 2, code 0x63 on isa0060/serio0).
[ 1918.995610] atkbd serio0: Use 'setkeycodes 63 <keycode>' to make it known.
[ 1919.032121] atkbd serio0: Unknown key released (translated set 2, code 0x63 on isa0060/serio0).
[ 1919.032135] atkbd serio0: Use 'setkeycodes 63 <keycode>' to make it known.
[ 1926.098414] atkbd serio0: Unknown key pressed (translated set 2, code 0x62 on isa0060/serio0).
[ 1926.098461] atkbd serio0: Use 'setkeycodes 62 <keycode>' to make it known.
[ 1926.146537] atkbd serio0: Unknown key released (translated set 2, code 0x62 on isa0060/serio0).
[ 1926.146583] atkbd serio0: Use 'setkeycodes 62 <keycode>' to make it known.

The "Ideapad extra buttons" driver alreadys sends f22 / f23 key-events
when the touchpad is toggles off, so map the keycodes for the duplicate
atkbd events to unknown to silence these kernel warnings.