[Feature]: Please document the CPUID leaves

### Feature Description
The CPUID instruction is documented as a bare operation, most of which is un-useful to programmers. The SDM does document the leaves.

Maybe don't document it as part of the instruction, but instead provide a separate section of the CPUID fields.

Bonus: document for each ISA extension which CPU generation it was first present in.

### Why Is This Needed?
When programming software that needs to know whether a specific CPU feature is present or query a specific information about it (cache sizes, topology, XSAVE capabilities, etc.), one uses the CPUID instruction. But we need to know what input to use and which bit fields to check.

Start by reviewing the existing CPUID instruction documentation and the corresponding SDM leaf descriptions. Decide how a separate CPUID-fields section fits the site, then track the requested input values and bit fields, with first CPU generations for ISA extensions where available. Done means the relevant leaves are documented and programmers can identify inputs and fields to query.

Written by the indexing model from the issue text.