Docs update: I2C Slave and APB GPIO

[cst-jayesht]

This PR includes documentation updates for the I2C Slave and APB GPIO modules. It adds updated images and expands key sections to improve clarity and completeness.

[MikeOpenHWGroup]

Hi @cst-jayesht. I am still in the process of reviewing this PR and should have my review completed by EoB today. In the meantime, you will need to be covered by the Eclipse Committer Agreement, please refer to CONTRIBUTING for more information.

[cst-jayesht]

Hi @MikeOpenHWGroup, I have implemented changes according to your feedback. Kindly review them.

[MikeOpenHWGroup]

The review is complete and approved for merge. I will postpone the merge until our (virtual) in-person review.

[MikeOpenHWGroup]

Thanks for this @cst-jayesht, and also thanks for taking care of the updates I requested. I will merge this in now and invite members of the community to review it as well.

Note that there is one failing check related to this pull-request, but it is a SystemVerilog lint check that is unrelated to the documentation in this pull-request.