iio: imu: Fix dependencies for !HAS_IOMEM archs

Not every arch has io memory.
While the driver has correct dependencies the select statement
will bypass the HAS_IOMEM dependency.
So, unbreak the build by rendering it into a real dependency.

Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>