arch: arc: fix the bug in prologue of sys call handling

* the old codes may not save the caller saved regs correctly,
  e.g. r7- r12. Because the sys call entry is called in the form
  of static inline function. The compiler optimizations may not save
  all the caller saved regs.

* new codes use the irq stack frame as the sys call frame and gurantee
  all the called saved regs are pushed and popped correctly.

* the side effect of new codes are more stack operations and a little
  overhead.

Signed-off-by: Wayne Ren <wei.ren@synopsys.com>