This patch creates the IIO configfs root group. The group
will appear under <mount-point>/iio/, usually /config/iio.

We introduce configfs support in IIO in order to be able to easily
create IIO objects from userspace. The first supported IIO objects
are triggers introduced with next patches.
Signed-off-by: NDaniel Baluta <daniel.baluta@intel.com>
Tested-by: NMatt Ranostay <matt.ranostay@intel>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>