HID: asus: Fix mute and touchpad-toggle keys on Medion Akoya E1239T

The mute key, is broken. All the consumer keys on the keyboard USB
interface work normally, except for mute which only sends press events
and never sends release events.

The touchpad key sends the otherwise unused input report with a report-id
of 5 on the touchpad interface. It too only sends press events. This also
requires extra special handling since the multi-touch touchpad events and
the KEY_F21 events for the touchpad toggle must not be send from the same
input_dev (userspace cannot handle this).

This commit adds special handlig for both, fixing these keys not working.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>