Add support for SPI AD3552R

[machschmitt]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Add support for standard SPI AD3552R DAC.

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

How has this been tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• [ ] Test A
• [ ] Test B

Test Configuration:

• Hardware:
• OS:

Documentation

If this is a new feature or example please mention or link any documentation. All new hardware interface classes require documentation.

Checklist:

• [ ] My code follows the style guidelines of this project
• [ ] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have signed off all commits and they contain "Signed-off by: "
• [ ] I have made corresponding changes to the documentation
• [ ] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes
• [ ] Any dependent changes have been merged and published in downstream modules

[machschmitt]

There is a new branch supporting upstream ad3552r and axi-ad3552r and cn0585. https://github.com/machschmitt/pyadi-iio/tree/spi_axi_ad3552r_cn0585 Closing this PR since ad3552r pyadi-iio support will be provided later when linux and pyadi-iio support for ad3552r reach a stable state.