powerpc/kconfig: define PAGE_SHIFT inside Kconfig

This patch defined CONFIG_PPC_PAGE_SHIFT in order
to be able to use PAGE_SHIFT value inside Kconfig.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/Kconfig

@@ -704,6 +704,13 @@ config PPC_256K_PAGES
 
 endchoice
 
+config PPC_PAGE_SHIFT
+	int
+	default 18 if PPC_256K_PAGES
+	default 16 if PPC_64K_PAGES
+	default 14 if PPC_16K_PAGES
+	default 12
+
 config THREAD_SHIFT
 	int "Thread shift" if EXPERT
 	range 13 15

arch/powerpc/include/asm/page.h

@@ -20,20 +20,11 @@
 
 /*
  * On regular PPC32 page size is 4K (but we support 4K/16K/64K/256K pages
- * on PPC44x). For PPC64 we support either 4K or 64K software
+ * on PPC44x and 4K/16K on 8xx). For PPC64 we support either 4K or 64K software
  * page size. When using 64K pages however, whether we are really supporting
  * 64K pages in HW or not is irrelevant to those definitions.
  */
-#if defined(CONFIG_PPC_256K_PAGES)
-#define PAGE_SHIFT		18
-#elif defined(CONFIG_PPC_64K_PAGES)
-#define PAGE_SHIFT		16
-#elif defined(CONFIG_PPC_16K_PAGES)
-#define PAGE_SHIFT		14
-#else
-#define PAGE_SHIFT		12
-#endif
-
+#define PAGE_SHIFT		CONFIG_PPC_PAGE_SHIFT
 #define PAGE_SIZE		(ASM_CONST(1) << PAGE_SHIFT)
 
 #ifndef __ASSEMBLY__