s390/mm: provide PAGE_SHARED define

Only needed to make some drivers compile...
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/pgtable.h

@@ -385,6 +385,7 @@ extern unsigned long MODULES_END;
 #define PAGE_RW		__pgprot(_PAGE_TYPE_RW)
 
 #define PAGE_KERNEL	PAGE_RW
+#define PAGE_SHARED	PAGE_KERNEL
 #define PAGE_COPY	PAGE_RO
 
 /*