ppc: Add support for AMCC 440EPx and 440GRx PPC's

This series of patches adds support to the AMCC 440EPx and 440GRx PPC's and the evaluation boards Sequoia and Rainier. It's still arch/ppc, so likely no chance of merging upstream. Mainly for completeness. When the 4xx support in arch/powerpc has stabilized a little we will try to move this support to arch/powerpc too.

Best regards,
Stefan