powerpc: Add TIF_NOTIFY_RESUME support for tracehook

This adds TIF_NOTIFY_RESUME support for powerpc.  When set,
we call tracehook_notify_resume() on the way to user mode.
This overloads do_signal() to do the work, but changes its
arguments to it has the TIF_* bits handy in a register and
drops the useless first argument that was always zero.

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/entry_32.S

@@ -1060,8 +1060,8 @@ do_user_signal:			/* r10 contains MSR_KERNEL here */
 	SAVE_NVGPRS(r1)
 	rlwinm	r3,r3,0,0,30
 	stw	r3,_TRAP(r1)
-2:	li	r3,0
-	addi	r4,r1,STACK_FRAME_OVERHEAD
+2:	addi	r3,r1,STACK_FRAME_OVERHEAD
+	mr	r4,r9
 	bl	do_signal
 	REST_NVGPRS(r1)
 	b	recheck