powerpc: Fix build error with 64K pages and !hugetlbfs

HAVE_ARCH_UNMAPPED_AREA and HAVE_ARCH_UNMAPPED_AREA_TOPDOWN must
be defined whenever CONFIG_PPC_MM_SLICES is enabled, not just when
CONFIG_HUGETLB_PAGE is.  They used to be always defined together but
this is no longer the case since 3a8247cc
("powerpc: Only demote individual slices rather than whole process").
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: NPaul Mackerras <paulus@samba.org>

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

@@ -153,12 +153,10 @@
 #define __S110	PAGE_SHARED_X
 #define __S111	PAGE_SHARED_X
 
-#ifdef CONFIG_HUGETLB_PAGE
-
+#ifdef CONFIG_PPC_MM_SLICES
 #define HAVE_ARCH_UNMAPPED_AREA
 #define HAVE_ARCH_UNMAPPED_AREA_TOPDOWN
-
-#endif
+#endif /* CONFIG_PPC_MM_SLICES */
 
 #ifndef __ASSEMBLY__