asm-generic: add dummy pgprot_noncached()

Most architectures now provide a pgprot_noncached(), the
remaining ones can simply use an dummy default implementation,
except for cris and xtensa, which should override the
default appropriately.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Jesper Nilsson <jesper.nilsson@axis.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: Magnus Damm <magnus.damm@gmail.com>

include/asm-generic/pgtable.h

@@ -129,6 +129,10 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addres
 #define move_pte(pte, prot, old_addr, new_addr)	(pte)
 #endif
 
+#ifndef pgprot_noncached
+#define pgprot_noncached(prot)	(prot)
+#endif
+
 #ifndef pgprot_writecombine
 #define pgprot_writecombine pgprot_noncached
 #endif