Since commit 80b6093b ("kbuild: add -Wundef to KBUILD_CPPFLAGS
for W=1 builds"), building with W=1 detects -Wundef warnings for
assembly code.

  $ make W=1 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf-  arch/arm/mm/
    [snip]
    AS      arch/arm/mm/cache-v7.o
  In file included from arch/arm/mm/cache-v7.S:17:
  arch/arm/mm/proc-macros.S:109:5: warning: "L_PTE_SHARED" is not defined, evaluates to 0 [-Wundef]
    109 | #if L_PTE_SHARED != PTE_EXT_SHARED
        |     ^~~~~~~~~~~~
  arch/arm/mm/proc-macros.S:109:21: warning: "PTE_EXT_SHARED" is not defined, evaluates to 0 [-Wundef]
    109 | #if L_PTE_SHARED != PTE_EXT_SHARED
        |                     ^~~~~~~~~~~~~~
  arch/arm/mm/proc-macros.S:113:10: warning: "L_PTE_XN" is not defined, evaluates to 0 [-Wundef]
    113 |         (L_PTE_XN+L_PTE_USER+L_PTE_RDONLY+L_PTE_DIRTY+L_PTE_YOUNG+\
        |          ^~~~~~~~
  arch/arm/mm/proc-macros.S:113:19: warning: "L_PTE_USER" is not defined, evaluates to 0 [-Wundef]
    113 |         (L_PTE_XN+L_PTE_USER+L_PTE_RDONLY+L_PTE_DIRTY+L_PTE_YOUNG+\
        |                   ^~~~~~~~~~
  arch/arm/mm/proc-macros.S:113:30: warning: "L_PTE_RDONLY" is not defined, evaluates to 0 [-Wundef]
    113 |         (L_PTE_XN+L_PTE_USER+L_PTE_RDONLY+L_PTE_DIRTY+L_PTE_YOUNG+\
        |                              ^~~~~~~~~~~~
  arch/arm/mm/proc-macros.S:113:43: warning: "L_PTE_DIRTY" is not defined, evaluates to 0 [-Wundef]
    113 |         (L_PTE_XN+L_PTE_USER+L_PTE_RDONLY+L_PTE_DIRTY+L_PTE_YOUNG+\
        |                                           ^~~~~~~~~~~
  arch/arm/mm/proc-macros.S:113:55: warning: "L_PTE_YOUNG" is not defined, evaluates to 0 [-Wundef]
    113 |         (L_PTE_XN+L_PTE_USER+L_PTE_RDONLY+L_PTE_DIRTY+L_PTE_YOUNG+\
        |                                                       ^~~~~~~~~~~
  arch/arm/mm/proc-macros.S:114:10: warning: "L_PTE_PRESENT" is not defined, evaluates to 0 [-Wundef]
    114 |          L_PTE_PRESENT) > L_PTE_SHARED
        |          ^~~~~~~~~~~~~
  arch/arm/mm/proc-macros.S:114:27: warning: "L_PTE_SHARED" is not defined, evaluates to 0 [-Wundef]
    114 |          L_PTE_PRESENT) > L_PTE_SHARED
        |                           ^~~~~~~~~~~~

Include <asm/pgtable.h> from proc-macros.S to fix the warnings.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>