sh: Fixup __strnlen_user() behaviour.

Drop TIF_USERSPACE and add addr_limit to the thread_info struct.
Subsequently, use that for address checking in strnlen_user() to
ward off bogus -EFAULTs.

Make __strnlen_user() return 0 on exception, rather than -EFAULT.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>

include/asm-sh/processor.h

@@ -149,6 +149,10 @@ struct thread_struct {
 	union sh_fpu_union fpu;
 };
 
+typedef struct {
+	unsigned long seg;
+} mm_segment_t;
+
 /* Count of active tasks with UBC settings */
 extern int ubc_usercnt;