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>

arch/arc/include/asm/ptrace.h

@@ -59,7 +59,6 @@ struct pt_regs {
 /* Callee saved registers - need to be saved only when you are scheduled out */
 
 struct callee_regs {
-	long res;	/* Again this is not needed */
 	long r25;
 	long r24;
 	long r23;