x86/ce4100: Fix pm_poweroff

The CE4100 platform is currently missing a proper pm_poweroff
implementation leading to poweroff making the CPU spin forever
and the CE4100 platform does not enter a low-power mode where
the external Power Management Unit can properly power off the
system. Power off on this platform is implemented pretty much
like reboot, by writing to the SoC built-in 8051 microcontroller
mapped at I/O port 0xcf9, the value 0x4.

Signed-off-by: Florian Fainelli <ffainelli@freebox.fr>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: rui.zhang@intel.com
Cc: alan@linux.intel.com
Link: http://lkml.kernel.org/r/1351518020-25556-2-git-send-email-ffainelli@freebox.fr
Signed-off-by: Ingo Molnar <mingo@kernel.org>