x86 platform drivers: hp-wmi Set placeholder for unimplemented events

Rather than print unknown events when we know what caused them

Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Matthew Garrett <mjg@redhat.com>
CC: linux-acpi@vger.kernel.org
CC: platform-driver-x86@vger.kernel.org