powerpc/32: Simplify EXCEPTION_PROLOG_1 macro

Make code more readable with a clear CONFIG_VMAP_STACK
section and a clear non CONFIG_VMAP_STACK section.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/c0f16cf432d22fc80097264d94649460d3dd761d.1606285014.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/head_32.h

@@ -46,18 +46,16 @@
 	mfspr	r1,SPRN_SPRG_THREAD
 	lwz	r1,TASK_STACK-THREAD(r1)
 	addi	r1, r1, THREAD_SIZE - INT_FRAME_SIZE
+1:
+	mtcrf	0x7f, r1
+	bt	32 - THREAD_ALIGN_SHIFT, stack_overflow
 #else
 	subi	r11, r1, INT_FRAME_SIZE		/* use r1 if kernel */
 	beq	1f
 	mfspr	r11,SPRN_SPRG_THREAD
 	lwz	r11,TASK_STACK-THREAD(r11)
 	addi	r11, r11, THREAD_SIZE - INT_FRAME_SIZE
-#endif
-1:
-	tophys_novmstack r11, r11
-#ifdef CONFIG_VMAP_STACK
-	mtcrf	0x7f, r1
-	bt	32 - THREAD_ALIGN_SHIFT, stack_overflow
+1:	tophys(r11, r11)
 #endif
 .endm