sparc64: Improvde documentation and readability of atomic backoff code.

Document what's going on in asm/backoff.h with a large and descriptive
comment.  Refer to it above the cpu_relax() definition in
asm/processor_64.h

Rename the pause patching section to have "3insn" in it's name like
the other patching sections do.

Based upon feedback from Sam Ravnborg.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/arch/sparc/kernel/entry.h b/arch/sparc/kernel/entry.h
index 51742df..cc3c5cb 100644
--- a/arch/sparc/kernel/entry.h
+++ b/arch/sparc/kernel/entry.h
@@ -63,8 +63,8 @@
 	unsigned int	addr;
 	unsigned int	insns[3];
 };
-extern struct pause_patch_entry __pause_patch,
-	__pause_patch_end;
+extern struct pause_patch_entry __pause_3insn_patch,
+	__pause_3insn_patch_end;
 
 extern void __init per_cpu_patch(void);
 extern void sun4v_patch_1insn_range(struct sun4v_1insn_patch_entry *,