arc/swap: add operation to save register r0 value.

when enable tracing, the register r0 which saves the return value
of __swap will be changed by sys_trace_thread_switched_in function,
casuing some unexpected return value, so use the stack to save
register r0 value.

Signed-off-by: peng1 chen <[email protected]>

Author: peng1 chen

arch/arc/core/swap.S

@@ -179,9 +179,11 @@ return_loc:
 #ifdef CONFIG_TRACING
 	push_s blink
 	push_s r1
+	push_s r0
 
 	bl sys_trace_thread_switched_in
 
+	pop_s r0
 	pop_s r1
 	pop_s blink
 #endif