powerpc: Make STRICT_MM_TYPECHECKS a config option

The STRICT_MM_TYPECHECKS code has bit-rotted over the years. To make it
possible to easily build test it, make it a CONFIG option.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/Kconfig.debug

@@ -19,6 +19,14 @@ config PPC_WERROR
 	depends on !PPC_DISABLE_WERROR
 	default y
 
+config STRICT_MM_TYPECHECKS
+	bool "Do extra type checking on mm types"
+	default n
+	help
+	  This option turns on extra type checking for some mm related types.
+
+	  If you don't know what this means, say N.
+
 config PRINT_STACK_DEPTH
 	int "Stack depth to print" if DEBUG_KERNEL
 	default 64

arch/powerpc/include/asm/page.h

@@ -278,9 +278,7 @@ extern long long virt_phys_offset;
 
 #ifndef __ASSEMBLY__
 
-#undef STRICT_MM_TYPECHECKS
-
-#ifdef STRICT_MM_TYPECHECKS
+#ifdef CONFIG_STRICT_MM_TYPECHECKS
 /* These are used to make use of C type-checking. */
 
 /* PTE level */

arch/powerpc/include/asm/pgtable-ppc64.h

@@ -118,7 +118,7 @@
  */
 #ifndef __real_pte
 
-#ifdef STRICT_MM_TYPECHECKS
+#ifdef CONFIG_STRICT_MM_TYPECHECKS
 #define __real_pte(e,p)		((real_pte_t){(e)})
 #define __rpte_to_pte(r)	((r).pte)
 #else