mm: add missing __PAGETABLE_{PUD,PMD}_FOLDED defines

Core mm expects __PAGETABLE_{PUD,PMD}_FOLDED to be defined if these page
table levels folded. Usually, these defines are provided by
<asm-generic/pgtable-nopmd.h> and <asm-generic/pgtable-nopud.h>.

But some architectures fold page table levels in a custom way. They
need to define these macros themself. This patch adds missing defines.

The patch fixes mm->nr_pmds underflow and eliminates dead __pmd_alloc()
and __pud_alloc() on architectures without these page table levels.

Signed-off-by: Kirill A. Shutemov <[e-mail]>
Cc: Aaro Koskinen <[e-mail]>
Cc: David Howells <[e-mail]>
Cc: Geert Uytterhoeven <[e-mail]>
Cc: Heiko Carstens <[e-mail]>
Cc: Helge Deller <[e-mail]>
Cc: "James E.J. Bottomley" <[e-mail]>
Cc: Koichi Yasutake <[e-mail]>
Cc: Martin Schwidefsky <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/frv/include/asm/pgtable.h

···
 #define PGDIR_MASK		(~(PGDIR_SIZE - 1))
 #define PTRS_PER_PGD		64
 
+#define __PAGETABLE_PUD_FOLDED
 #define PUD_SHIFT		26
 #define PTRS_PER_PUD		1
 #define PUD_SIZE		(1UL << PUD_SHIFT)
 #define PUD_MASK		(~(PUD_SIZE - 1))
 #define PUE_SIZE		256
 
+#define __PAGETABLE_PMD_FOLDED
 #define PMD_SHIFT		26
 #define PMD_SIZE		(1UL << PMD_SHIFT)
 #define PMD_MASK		(~(PMD_SIZE - 1))

arch/m32r/include/asm/pgtable-2level.h

···
  * the M32R is two-level, so we don't really have any
  * PMD directory physically.
  */
+#define __PAGETABLE_PMD_FOLDED
 #define PMD_SHIFT	22
 #define PTRS_PER_PMD	1
 

arch/m68k/include/asm/pgtable_mm.h

···
  */
 #ifdef CONFIG_SUN3
 #define PTRS_PER_PTE   16
+#define __PAGETABLE_PMD_FOLDED
 #define PTRS_PER_PMD   1
 #define PTRS_PER_PGD   2048
 #elif defined(CONFIG_COLDFIRE)
 #define PTRS_PER_PTE	512
+#define __PAGETABLE_PMD_FOLDED
 #define PTRS_PER_PMD	1
 #define PTRS_PER_PGD	1024
 #else

arch/mn10300/include/asm/pgtable.h

···
 #define PGDIR_SHIFT	22
 #define PTRS_PER_PGD	1024
 #define PTRS_PER_PUD	1	/* we don't really have any PUD physically */
+#define __PAGETABLE_PUD_FOLDED
 #define PTRS_PER_PMD	1	/* we don't really have any PMD physically */
+#define __PAGETABLE_PMD_FOLDED
 #define PTRS_PER_PTE	1024
 
 #define PGD_SIZE	PAGE_SIZE

arch/parisc/include/asm/pgtable.h

···
 #if PT_NLEVELS == 3
 #define BITS_PER_PMD	(PAGE_SHIFT + PMD_ORDER - BITS_PER_PMD_ENTRY)
 #else
+#define __PAGETABLE_PMD_FOLDED
 #define BITS_PER_PMD	0
 #endif
 #define PTRS_PER_PMD    (1UL << BITS_PER_PMD)

arch/s390/include/asm/pgtable.h

···
  */
 #define PTRS_PER_PTE	256
 #ifndef CONFIG_64BIT
+#define __PAGETABLE_PUD_FOLDED
 #define PTRS_PER_PMD	1
+#define __PAGETABLE_PMD_FOLDED
 #define PTRS_PER_PUD	1
 #else /* CONFIG_64BIT */
 #define PTRS_PER_PMD	2048