powerpc: change CONFIG_PPC_STD_MMU_32 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 PPC_STD_MMU
	def_bool y
	depends on PPC_BOOK3S

config PPC_STD_MMU_32
	def_bool y
	depends on PPC_STD_MMU && PPC32

PPC_STD_MMU_32 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_PPC_STD_MMU_32 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/mm/pgtable_32.c

@@ -260,7 +260,7 @@ static void __init __mapin_ram_chunk(unsigned long offset, unsigned long top)
 		ktext = ((char *)v >= _stext && (char *)v < etext) ||
 			((char *)v >= _sinittext && (char *)v < _einittext);
 		map_kernel_page(v, p, ktext ? PAGE_KERNEL_TEXT : PAGE_KERNEL);
-#ifdef CONFIG_PPC_STD_MMU_32
+#ifdef CONFIG_PPC_BOOK3S_32
 		if (ktext)
 			hash_preload(&init_mm, v, false, 0x300);
 #endif