powerpc: change CONFIG_6xx to CONFIG_PPC_BOOK3S_32

Today we have:

config PPC_BOOK3S_32
	bool "512x/52xx/6xx/7xx/74xx/82xx/83xx/86xx"
	[depends on PPC32 within a choice]

config PPC_BOOK3S
	def_bool y
	depends on PPC_BOOK3S_32 || PPC_BOOK3S_64

config 6xx
	def_bool y
	depends on PPC32 && PPC_BOOK3S

6xx is therefore redundant with PPC_BOOK3S_32.

In order to make the code clearer, lets use preferably PPC_BOOK3S_32.
This will allow to remove CONFIG_6xx in a later patch.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/head_32.S

@@ -176,10 +176,10 @@ __after_mmu_off:
 	bl	reloc_offset
 	li	r24,0			/* cpu# */
 	bl	call_setup_cpu		/* Call setup_cpu for this CPU */
-#ifdef CONFIG_6xx
+#ifdef CONFIG_PPC_BOOK3S_32
 	bl	reloc_offset
 	bl	init_idle_6xx
-#endif /* CONFIG_6xx */
+#endif /* CONFIG_PPC_BOOK3S_32 */
 
 
 /*
@@ -836,10 +836,10 @@ __secondary_start:
 	lis	r3,-KERNELBASE@h
 	mr	r4,r24
 	bl	call_setup_cpu		/* Call setup_cpu for this CPU */
-#ifdef CONFIG_6xx
+#ifdef CONFIG_PPC_BOOK3S_32
 	lis	r3,-KERNELBASE@h
 	bl	init_idle_6xx
-#endif /* CONFIG_6xx */
+#endif /* CONFIG_PPC_BOOK3S_32 */
 
 	/* get current_thread_info and current */
 	lis	r1,secondary_ti@ha
@@ -880,14 +880,14 @@ __secondary_start:
 
 /*
  * Those generic dummy functions are kept for CPUs not
- * included in CONFIG_6xx
+ * included in CONFIG_PPC_BOOK3S_32
  */
-#if !defined(CONFIG_6xx)
+#if !defined(CONFIG_PPC_BOOK3S_32)
 _ENTRY(__save_cpu_setup)
 	blr
 _ENTRY(__restore_cpu_setup)
 	blr
-#endif /* !defined(CONFIG_6xx) */
+#endif /* !defined(CONFIG_PPC_BOOK3S_32) */
 
 
 /*