iio: dac: support the ad9739a RF DAC

The AD9739A is a 14-bit, 2.5 GSPS high performance RF DACs that are capable
of synthesizing wideband signals from DC up to 3 GHz.

A dual-port, source synchronous, LVDS interface simplifies the digital
interface with existing FGPA/ASIC technology. On-chip controllers are used
to manage external and internal clock domain variations over temperature to
ensure reliable data transfer from the host to the DAC core.

Co-developed-by: Dragos Bogdan <dragos.bogdan@analog.com>
Signed-off-by: Dragos Bogdan <dragos.bogdan@analog.com>
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20240419-iio-backend-axi-dac-v4-10-5ca45b4de294@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>