powerpc/44x: Removing dead CONFIG_PPC47x

CONFIG_PPC47x doesn't exist in Kconfig and no 476 processor calls this
function ppc44x_pin_tlb() as it has it's own ppc47x_pin_tlb().

This code is probably an artifact of the original 476 code that
shouldn't have made it upstream.

Signed-off-by: Christoph Egger <siccegge@cs.fau.de>
Signed-off-by: Tony Breeds <tony@bakeyournoodle.com>
Signed-off-by: Josh Boyer <jwboyer@gmail.com>