[PATCH] ppc32: fix perf_irq extern on e500

Fixes e500 build and cleans up traps.c by moving perf_irq extern to
pmc.h.

Signed-off-by: Matt Porter <mporter@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>