AltiVec register ptrace support

[Paul Mackerras]

Andrew Cagney writes:

> The Linux/PPC kernel supports PEEK/POKE for fetching registers.  The 
> proposed Kernel interface _consistently_ extends that interface using 
> the exact same mechanims to obtain the altivec regiters.  All the 
> required changes for this have been posted and have been demonstrated to 
> work.
> 
> Separate to that, it has been _proposed_ that the PPC ptrace() interface 
> be changed so that get/set reg for all register classes be added 
> (incomplete patch posted).  Isn't this separate to the problem at hand?

If we are going to add a get/set reg interface for the altivec vector
registers, I would rather not extend the peek/poke interface to do
that as well.

Paul.