powerpc/32: Fix compile error caused by pud_t/pgt_t confusion

PPC32 is still using asm-generic/4level-fixup.h, but asm-powerpc/page.h
was defining pud_t and pgd_t.  Depending on the order in which files
got included, this could result in a compilation error.  Tweak the ifdef
so that page.h doesn't try to define pud_t on ppc32 (which uses 2-level
page tables).
Signed-off-by: NPaul Mackerras <paulus@samba.org>

include/asm-powerpc/page.h

@@ -178,7 +178,7 @@ typedef unsigned long pmd_t;
 #define pmd_val(x)	(x)
 #define __pmd(x)	(x)
 
-#ifndef CONFIG_PPC_64K_PAGES
+#if defined(CONFIG_PPC64) && !defined(CONFIG_PPC_64K_PAGES)
 typedef unsigned long pud_t;
 #define pud_val(x)	(x)
 #define __pud(x)	(x)