Renamed LWM2M_RD_CLIENT_EVENT_REG_UPDATE_FAILURE to
LWM2M_RD_CLIENT_EVENT_REG_TIMEOUT.
Changed reported event type for registration timeout to
LWM2M_RD_CLIENT_EVENT_REG_TIMEOUT from
LWM2M_RD_CLIENT_EVENT_REGISTRATION_FAILURE.
LWM2M_RD_CLIENT_EVENT_REGISTRATION_FAILURE should be only
reported case when server reject by response registration.
Signed-off-by: Juha Heiskanen <juha.heiskanen@nordicsemi.no>