[FEATURE] Document how the ARM should respond to keyboard single byte response commands

[RichardBrown384]

Is your feature request related to a problem? Please describe.
How is the CPU is supposed to respond to the keyboard data request or a keyboard id responses? This is not documented in an A3000 service manual.

Describe the solution you'd like
These two cases to be investigated and the correct behaviour implemented. The current behaviour appears to work but it might not be the most correct and the Operating System might be resilient enough to work around an incorrect implementation.

Describe alternatives you've considered
N/A

Additional context
The A3000 service manual gives that part number for the keyboard controller chip as (0708,051). Other sources say this is an Intel 8051, maybe there's additional information about the protocol elsewhere.