reference-designs/ad9695_fmc: Add AD9695_FMC documentation

[BCapota]

Type

• Documentation
• Bug fix
• New feature
• Continuous integration

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[gastmaier]

Suggested change

	.. _ad9695 ebz:
	.. _ad9695-fmc:

.. _ad9695-fmc user-guide:

.. _ad9695-fmc help:

[StancaPop]

This is the HDL block diagram. Replace it with this one https://www.analog.com/en/products/ad9695.html

[IuliaCMoldovan]

We should mention that the use of Synchrona is optional.
The users can use a clock generator with multiple outputs. So mark them with a star or something like that, that Synchrona, the GPIO module, the cable, and the terminators are optional.

[BCapota]

I updated the documentation to clarify that Synchrona and the related components are optional and added a note about using a multiple outputs clock generator as an alternative. Thank you!

[StancaPop]

Looks good to me. Needs technical review from @IuliaCMoldovan.