Add AXI-AD3552R

[machschmitt]

Add the AXI-AD3585R DAC driver which adapts AD3585R for use with ad3552r_evb HDL project.

Comments:

• Add AXI-AD3585R platform driver.
• dt-binding documentation leveraged by upstream version.
• There is a second HDL project which uses the AXI-AD3585R driver and that one also depends on updated versions of MathWorks drivers from PR drivers:misc:mathworks: Sync MathWorks drivers #2193. I left the changes related to that project to a follow-up PR.

[machschmitt]

Update: removed unused device tree properties from the axi-ad3552r_evb dts file and from the dt-binding doc.

[nunojsa]

Before jumping in reviewing, How is this supposed to work with the real HW DAC? Asking it because typically you have the converter/frontend (in this case a DAC) wich connects to a backend (the hdl IP) and that backend is cf_axi_dds.

At first glance I can see that there are a fairly amount of specific registers for this core but I'm still trying to understand if extending cf_axi_dds.c was considered or if it makes any sense to do so?

I just want to avoid having code duplication all over the place if we start implementing these projects like this (typically we use the above "arrangement").

[machschmitt]

At first glance I can see that there are a fairly amount of specific registers for this core but I'm still trying to understand if extending cf_axi_dds.c was considered or if it makes any sense to do so?

Apparently yes, the cf_axi_dds driver could be extended to also support ad3552r. So I'm working on that refactoring/extension now. Meanwhile, let's turn this into a draft.