[patch, sim] Add isel instruction

[Joel Brobecker]

> sim/ppc/ChangeLog:
> 2013-05-03  Hafiz Abid Qadeer  <abidh@codesourcery.com>
> 
> 	revert:
> 	2013-04-19  Nathan Froyd  <froydnj@codesourcery.com>
> 	* ppc-instructions (isel): New instruction.

Thanks!

For the record, I also moved the original ChangeLog entry from
sim/ChangeLog to sim/ppc/ChangeLog.

-- 
Joel