[Hafnium] Manifest bindings

Hi,

https://hafnium.readthedocs.io/en/latest/design/ffa-manifest-binding.html has a nice description of the manifest bindings. The intention is obviously to match the fields in the FF-A specification. However, the "pages-count" field in the bindings is called "page count" in the specification. Any chance of fixing this so the two fields have the same name?

Thanks, Jens