iio: light: add MAX30100 oximeter driver support

MAX30100 is an heart rate and pulse oximeter sensor that works using
two LEDS of different wavelengths, and detecting the light reflected
back.

This patchset adds support for both IR and RED LED channels which can
be processed in userspace to determine heart rate and blood oxygen
levels.

Signed-off-by: Matt Ranostay <mranostay@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>