ARC: pt_regs update #3: Remove unused gutter at start of callee_regs

This is trickier than prev two:

* context switching code saves kernel mode callee regs in the format of
  struct callee_regs thus needs adjustment. This also reduces the height
  of topmost kernel stack frame by 1 word.

* Since kernel stack unwinder is sensitive to height of topmost kernel
  stack frame, that needs a word of adjustment too.

ptrace needs a bit of updating since pt_regs now diverges from
user_regs_struct.

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
diff --git a/arch/arc/kernel/stacktrace.c b/arch/arc/kernel/stacktrace.c
index ca0207b..f8b7d88 100644
--- a/arch/arc/kernel/stacktrace.c
+++ b/arch/arc/kernel/stacktrace.c
@@ -79,7 +79,7 @@
 		 * assembly code
 		 */
 		frame_info->regs.r27 = 0;
-		frame_info->regs.r28 += 64;
+		frame_info->regs.r28 += 60;
 		frame_info->call_frame = 0;
 
 	} else {