iio: frequency: adf4350: add clk provider

iio: frequency: adf4350: add clk provider

Add clk provider feature for the adf4350.

Even though the driver was sent as an IIO driver in most cases the
device is actually seen as a clock provider.

This patch aims to cover actual usecases requested by users in order to
completely control the output frequencies from userspace.

Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Link: https://patch.msgid.link/20240621121403.47912-2-antoniu.miclaus@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>