m32r/kernel/: cleanups

This patch contains the following cleanups:
- make the following needlessly global code static:
  - entry.S: resume_userspace
  - process.c: pm_idle
  - process.c: default_idle()
  - smp.c: send_IPI_allbutself()
  - time.c: timer_interrupt()
  - time.c: struct irq0
  - traps.c: set_eit_vector_entries()
  - traps.c: kstack_depth_to_print
  - traps.c: show_trace()
  - traps.c: die_lock
- remove the following unused code:
  - head.S: startup_32
  - process.c: hlt_counter
  - process.c: disable_hlt()
  - process.c: enable_hlt()
  - process.c: dump_task_regs()
- remove the following variables and their usages since they were
  always 0:
  - irq.c: irq_err_count
  - irq.c: irq_mis_count

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Hirokazu Takata <takata@linux-m32r.org>