AUDIT: make audit_is_compat depend on CONFIG_AUDIT_COMPAT_GENERIC

On systems with CONFIG_COMPAT we introduced the new requirement that
audit_classify_compat_syscall() exists.  This wasn't true for everything
(apparently not for "tilegx", which I know less that nothing about.)

Instead of wrapping the preprocessor optomization with CONFIG_COMPAT we
should have used the new CONFIG_AUDIT_COMPAT_GENERIC.  This patch uses
that config option to make sure only arches which intend to implement
this have the requirement.

This works fine for tilegx according to Chris Metcalf
Signed-off-by: NEric Paris <eparis@redhat.com>

include/linux/audit.h

@@ -102,7 +102,7 @@ struct filename;
 
 extern void audit_log_session_info(struct audit_buffer *ab);
 
-#ifdef CONFIG_COMPAT
+#ifdef CONFIG_AUDIT_COMPAT_GENERIC
 #define audit_is_compat(arch)  (!((arch) & __AUDIT_ARCH_64BIT))
 #else
 #define audit_is_compat(arch)  false