powerpc/47x: Use the new ppc-opcode infrastructure

Don't use 47x only #defines for TLBIVAX or ICBT, supply and use helpers
in ppc-opcode.h

This fixes a compile breakage.

Signed-off-by: Tony Breeds <tony@bakeyournoodle.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>