Pull the code to generalize the powerpc VIRQ_DEBUG code from Grant Likely.

That code had been moved into generic irqdomain code, but still had
powerpc-specific code and could only be enabled on powerpc.

* 'irqdomain/merge' of git://git.secretlab.ca/git/linux-2.6:
  irqdomain/powerpc: updated defconfigs for VIRQ_DEBUG rename
  irqdomain: Remove powerpc dependency from debugfs file