i2c-omap: fix static suspend vs. runtime suspend

When runtime PM is enabled, each OMAP i2c device is suspended after
each i2c xfer.  However, there are two cases when the static suspend
methods must be used to ensure the devices are suspended:

1) runtime PM is disabled, either at compile time or dynamically
    via /sys/devices/.../power/control.
2) an i2c client driver uses i2c during it's suspend callback, thus
   leaving the i2c driver active (NOTE: runtime suspend transitions are
   disabled during system suspend, so i2c activity during system
   suspend will runtime resume the device, but not runtime (re)suspend it.)

Since the actual work to suspend the device is handled by the
subsytem, call the bus methods to take care of it.

NOTE: This takes care of a known suspend problem on OMAP3 where the
TWL RTC driver does i2c xfers during its suspend path leaving the i2c
driver in an active state (since runtime suspend transistions are
disabled.)

Signed-off-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>