powerpc/book3s_32: Fix build error with checkpoint restart

In file included from mm/vmscan.c:54:0:
include/linux/swapops.h: In function ‘pte_to_swp_entry’:
include/linux/swapops.h:69:2: error: implicit declaration of function ‘pte_swp_soft_dirty’ [-Werror=implicit-function-declaration]
  if (pte_swp_soft_dirty(pte))
  ^
include/linux/swapops.h:70:3: error: implicit declaration of function ‘pte_swp_clear_soft_dirty’ [-Werror=implicit-function-declaration]
   pte = pte_swp_clear_soft_dirty(pte);

We support soft dirty tracking only with book3s 64 for now.
So change the Kconfig dependency accordingly. Also CHECKPOINT_RESTORE
feature is not really dependent on SOFT_DIRTY. We track the dependency
between MEM_SOFT_DIRTY and ARCH_SOFT_DIRTY through headers

Fixes: 7207f436 ("powerpc/mm: Add page soft dirty tracking")
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/Kconfig

@@ -557,7 +557,7 @@ choice
 
 config PPC_4K_PAGES
 	bool "4k page size"
-	select HAVE_ARCH_SOFT_DIRTY if CHECKPOINT_RESTORE && PPC_BOOK3S
+	select HAVE_ARCH_SOFT_DIRTY if PPC_BOOK3S_64
 
 config PPC_16K_PAGES
 	bool "16k page size"
@@ -566,7 +566,7 @@ config PPC_16K_PAGES
 config PPC_64K_PAGES
 	bool "64k page size"
 	depends on !PPC_FSL_BOOK3E && (44x || PPC_STD_MMU_64 || PPC_BOOK3E_64)
-	select HAVE_ARCH_SOFT_DIRTY if CHECKPOINT_RESTORE && PPC_BOOK3S
+	select HAVE_ARCH_SOFT_DIRTY if PPC_BOOK3S_64
 
 config PPC_256K_PAGES
 	bool "256k page size"