powerpc/32: Add vmap_stack_overflow label inside the macro

For consistency, add in the macro the label used by exception prolog
to branch to stack overflow processing.

While at it, enclose the macro in #ifdef CONFIG_VMAP_STACK on the 8xx
as already done on book3s/32.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/cf80056f5b946572ad98aea9d915dd25b23beda6.1615552867.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/head_32.h

@@ -52,7 +52,7 @@
 1:
 #ifdef CONFIG_VMAP_STACK
 	mtcrf	0x3f, r1
-	bt	32 - THREAD_ALIGN_SHIFT, stack_overflow
+	bt	32 - THREAD_ALIGN_SHIFT, vmap_stack_overflow
 #endif
 .endm
 
@@ -196,6 +196,7 @@ label:
 			  ret_from_except)
 
 .macro vmap_stack_overflow_exception
+vmap_stack_overflow:
 #ifdef CONFIG_SMP
 	mfspr	r1, SPRN_SPRG_THREAD
 	lwz	r1, TASK_CPU - THREAD(r1)

arch/powerpc/kernel/head_8xx.S

@@ -338,8 +338,9 @@ DARFixed:/* Return from dcbx instruction bug workaround */
 	/* 0x300 is DataAccess exception, needed by bad_page_fault() */
 	EXC_XFER_LITE(0x300, handle_page_fault)
 
-stack_overflow:
+#ifdef CONFIG_VMAP_STACK
 	vmap_stack_overflow_exception
+#endif
 
 /* On the MPC8xx, these next four traps are used for development
  * support of breakpoints and such.  Someday I will get around to

arch/powerpc/kernel/head_book3s_32.S

@@ -732,7 +732,6 @@ fast_hash_page_return:
 #endif /* CONFIG_PPC_BOOK3S_604 */
 
 #ifdef CONFIG_VMAP_STACK
-stack_overflow:
 	vmap_stack_overflow_exception
 #endif