powerpc: Fix various issues with return to userspace

We have a few problems when returning to userspace. This is a
quick set of fixes for 3.3, I'll look into a more comprehensive
rework for 3.4. This fixes:

 - We kept interrupts soft-disabled when schedule'ing or calling
do_signal when returning to userspace as a result of a hardware
interrupt.

 - Rename do_signal to do_notify_resume like all other archs (and
do_signal_pending back to do_signal, which it was before Roland
changed it).

 - Add the missing call to key_replace_session_keyring() to
do_notify_resume().

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index d834425..866462c 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -751,12 +751,16 @@
 
 	andi.	r0,r4,_TIF_NEED_RESCHED
 	beq	1f
+	li	r5,1
+	TRACE_AND_RESTORE_IRQ(r5);
 	bl	.schedule
 	b	.ret_from_except_lite
 
 1:	bl	.save_nvgprs
+	li	r5,1
+	TRACE_AND_RESTORE_IRQ(r5);
 	addi	r3,r1,STACK_FRAME_OVERHEAD
-	bl	.do_signal
+	bl	.do_notify_resume
 	b	.ret_from_except
 
 unrecov_restore: