powerpc: merge idle_power4.S and trapc.s

Use idle_power4.S from ppc64 as we are not going to support
32 bit power4 in the merged tree.

Merge ppc64 traps.c into powerpc traps.c:
	use ppc64 versions of exception routine names
		(as they don't have StudlyCaps)
	make all the versions if die() have the same
		prototype

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>