CONFIG_IIO is not available for the default architecture x86.
Result is shown for architecture avr32

Industrial I/O support

modulename: industrialio.ko
configname: CONFIG_IIO

Linux Kernel Configuration
└─> Device Drivers
└─> Industrial I/O support

The industrial I/O subsystem provides a unified framework for
drivers for many different types of embedded sensors using a
number of different physical interfaces (i2c, spi, etc).

source code: