ARC: Remove explicit passing around of ECR

With ECR now part of pt_regs

* No need to propagate from lowest asm handlers as arg
* No need to save it in tsk->thread.cause_code
* Avoid bit chopping to access the bit-fields

More code consolidation, cleanup

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/mm/tlbex.S

@@ -382,7 +382,6 @@ do_slow_path_pf:
 	; ------- setup args for Linux Page fault Hanlder ---------
 	mov_s r0, sp
 	lr  r1, [efa]
-	lr  r2, [ecr]
 
 	; We don't want exceptions to be disabled while the fault is handled.
 	; Now that we have saved the context we return from exception hence