iio:adc:ti-tlc4541: Drop CONFIG_OF and of_match_ptr protections.

These stop us using ACPI PRP0001 to instantiate the device.
I am slowly clearly out use of these in IIO to avoid this being coppied
into new drivers.

Here I also included mod_devicetable.h as we are using of_match_id
which is defined in there and hence it is best practice to include
it directly.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Phil Reid <preid@electromag.com.au>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>