RTC settings will be lost if power supply is cut off after hibernation
finished, but the current "restore" function does not restore RTC related
settings, this causes rtc_read_time failure and kernel panic:

  rtc rtc0: **** DPM device timeout ****
  Stack trace:
    unwind_backtrace+0x0/0xf4
    show_stack+0x10/0x14
    dpm_wd_handler+0x24/0x28
    call_timer_fn.isra.33+0x24/0x88
    run_timer_softirq+0x178/0x1f0
    __do_softirq+0x120/0x200
    do_softirq+0x54/0x5c
    irq_exit+0x9c/0xd0
    handle_IRQ+0x44/0x90
    __irq_svc+0x40/0x70
    _raw_spin_unlock_irqrestore+0x10/0x48
    sirfsoc_rtc_iobrg_readl+0x34/0x3c
    sirfsoc_rtc_read_time+0x24/0x48
    __rtc_read_time.isra.3+0x48/0x5c
    rtc_read_time+0x30/0x44
    rtc_resume.part.9+0x20/0x104
    rtc_resume+0x5c/0x64
    dpm_run_callback.isra.4+0x2c/0x74
    device_resume+0x9c/0x144
    dpm_resume+0x100/0x224
    hibernation_snapshot+0x170/0x398
    hibernate+0x13c/0x1d8
    state_store+0xb4/0xb8
    kobj_attr_store+0x14/0x20
    sysfs_write_file+0x160/0x190
    vfs_write+0xb4/0x194
    SyS_write+0x3c/0x78

this patch uses SIMPLE_DEV_PM_OPS() to make restore() execute the
existing resume() function which will restore the set of RTC.

Signed-off-by: Xianglong Du <Xianglong.Du@csr.com>
Signed-off-by: Barry Song <Baohua.Song@csr.com>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Rob Herring <robh+dt@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>