Largely inspired by the TMP105 temperature sensor, here is a model for
the TMP42{1,2,3} temperature sensors.

Specs can be found here :

	http://www.ti.com/lit/gpn/tmp421Signed-off-by: NCédric Le Goater <clg@kaod.org>
Message-id: 1496739230-32109-2-git-send-email-clg@kaod.org
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>