platform/x86: thinkpad_acpi: Add hotkey_notify_extended_hotkey() helper

Factor the extended hotkey handling out of hotkey_notify_hotkey() and
into a new hotkey_notify_extended_hotkey() helper.

This is a preparation patch for adding support the privacy-screen hotkey
toggle (which needs some special handling, it should NOT send an evdev
key-event to userspace...).

Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Mark Pearson <markpearson@lenovo.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211005202322.700909-7-hdegoede@redhat.com