powerpc/40x: Reorder a few instructions in critical exception prolog

In order to ease preparation for CONFIG_VMAP_STACK, reorder
a few instruction, especially save r1 into stack frame earlier.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/c895ecf958c86d1736bdd2ff6f36626b55f35fd2.1615552866.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/head_40x.S

@@ -119,6 +119,9 @@ _ENTRY(saved_ksp_limit)
 	lwz	r11,TASK_STACK-THREAD(r11) /* this thread's kernel stack */
 1:	addi	r11,r11,THREAD_SIZE-INT_FRAME_SIZE /* Alloc an excpt frm  */
 	tophys(r11,r11)
+	stw	r1,GPR1(r11)
+	stw	r1,0(r11)
+	tovirt(r1,r11)
 	stw	r10,_CCR(r11)		/* save various registers	   */
 	stw	r12,GPR12(r11)
 	stw	r9,GPR9(r11)
@@ -129,14 +132,11 @@ _ENTRY(saved_ksp_limit)
 	stw	r10,GPR10(r11)
 	stw	r12,GPR11(r11)
 	mfspr	r12,SPRN_DEAR		/* save DEAR and ESR in the frame  */
-	stw	r12,_DEAR(r11)		/* since they may have had stuff   */
 	mfspr	r9,SPRN_ESR		/* in them at the point where the  */
+	stw	r12,_DEAR(r11)		/* since they may have had stuff   */
 	stw	r9,_ESR(r11)		/* exception was taken		   */
 	mfspr	r12,SPRN_SRR2
-	stw	r1,GPR1(r11)
 	mfspr	r9,SPRN_SRR3
-	stw	r1,0(r11)
-	tovirt(r1,r11)
 	rlwinm	r9,r9,0,14,12		/* clear MSR_WE (necessary?)	   */
 	stw	r0,GPR0(r11)
 	lis	r10, STACK_FRAME_REGS_MARKER@ha /* exception frame marker */