powerpc/mm: Define platform default caches related flags

Cache related flags like _PAGE_COHERENT and _PAGE_WRITETHRU
are defined on most platforms. The platforms not defining
them don't define any alternative. So we can give them a NUL
value directly for those platforms directly.

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/nohash/32/pte-40x.h

@@ -53,6 +53,9 @@
 /* No page size encoding in the linux PTE */
 #define _PAGE_PSIZE		0
 
+/* cache related flags non existing on 40x */
+#define _PAGE_COHERENT	0
+
 #define _PAGE_KERNEL_RO		0
 #define _PAGE_KERNEL_ROX	_PAGE_EXEC
 #define _PAGE_KERNEL_RW		(_PAGE_DIRTY | _PAGE_RW | _PAGE_HWWRITE)

arch/powerpc/include/asm/nohash/32/pte-8xx.h

@@ -46,6 +46,10 @@
 #define _PAGE_NA	0x0200	/* Supervisor NA, User no access */
 #define _PAGE_RO	0x0600	/* Supervisor RO, User no access */
 
+/* cache related flags non existing on 8xx */
+#define _PAGE_COHERENT	0
+#define _PAGE_WRITETHRU	0
+
 #define _PAGE_KERNEL_RO		(_PAGE_PRIVILEGED | _PAGE_RO)
 #define _PAGE_KERNEL_ROX	(_PAGE_PRIVILEGED | _PAGE_RO | _PAGE_EXEC)
 #define _PAGE_KERNEL_RW		(_PAGE_PRIVILEGED | _PAGE_DIRTY)

arch/powerpc/include/asm/pte-common.h

@@ -1,17 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /* Included from asm/pgtable-*.h only ! */
 
-/*
- * Some bits are only used on some cpu families... Make sure that all
- * the undefined gets a sensible default
- */
-#ifndef _PAGE_COHERENT
-#define _PAGE_COHERENT	0
-#endif
-#ifndef _PAGE_WRITETHRU
-#define _PAGE_WRITETHRU	0
-#endif
-
 /* Location of the PFN in the PTE. Most 32-bit platforms use the same
  * as _PAGE_SHIFT here (ie, naturally aligned).
  * Platform who don't just pre-define the value so we don't override it here