iio: humidity: hdc100x: add HDC1000 and HDC1008 to Kconfig

hdc100x supports Texas Instruments HDC1000 and HDC1008 relative
humidity and temperature sensors. Add these product names to
Kconfig.

Signed-off-by: Alison Schofield <amsfield22@gmail.com>
Cc: Daniel Baluta <daniel.baluta@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>