metag: ptrace: Implement NT_METAG_TLS

Implement functionality to get the TLS pointer for the metag
architecture using regsets.

This provides multi-threaded debug support for GDB.

Signed-off-by: Paul Clothier <Paul.Clothier@imgtec.com>
Signed-off-by: James Hogan <james.hogan@imgtec.com>
diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
index 8072d35..ef6103b 100644
--- a/include/uapi/linux/elf.h
+++ b/include/uapi/linux/elf.h
@@ -397,6 +397,7 @@
 #define NT_ARM_HW_WATCH	0x403		/* ARM hardware watchpoint registers */
 #define NT_METAG_CBUF	0x500		/* Metag catch buffer registers */
 #define NT_METAG_RPIPE	0x501		/* Metag read pipeline state */
+#define NT_METAG_TLS	0x502		/* Metag TLS pointer */
 
 
 /* Note header in a PT_NOTE section */