iio: si7020: add support for Hoperf th06

This patch adds support for Hoperf th06 humidity and
temperature sensor as it uses same register definitions
as si7020

th06 Datasheet: http://www.hoperf.com/upload/sensor/TH06.pdf



Signed-off-by: Cristina Moraru <cristina.moraru09@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>