sh: SuperH Mobile Software Standby support for cpuidle

This patch adds "SuperH Mobile Standby Mode [SF]" to the list
of cpuidle sleep modes. If the software latency requirements
from cpuidle are met together with fulfilled hardware
requirements then deep sleep modes can be entered.

Tested on sh7722 and sh7724 with "Sleep Mode", "Sleep Mode + SF"
and "Software Standby Mode + SF" together with a multimedia
work load and flood ping without packet drop.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>