iio:adc:ti-adc0832: drop CONFIG_OF and of_match_ptr protections

These just prevent the driver being used with ACPI PRP0001.

I am also trying to remove these from IIO in general to avoid
them being coppied into new drivers.

Also include the mod_devicetable.h header as we are using
of_device_id which is defined in there.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>