iio: documentation: Add ABI documentation for *_mean_raw
iio: documentation: Add ABI documentation for *_mean_raw

Add ABI documentation for in_*_mean_raw files, which are
already supported and used in the kernel for some time.

Signed-off-by: Sebastian Reichel <1ea78bda3cb6d36efdb8fc89aad6555e21b4887e@debian.org>
Signed-off-by: Jonathan Cameron <09f65b71b7655725897b2fd41a09a0cefe2e1ace@kernel.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs