net: davinci_mdio: add hibernation callbacks

Setting a dev_pm_ops suspend_late/resume_early pair but not a
set of hibernation functions means those pm functions will
not be called upon hibernation.
Fix this by using SET_LATE_SYSTEM_SLEEP_PM_OPS, which appropriately
assigns the suspend and hibernation handlers and move
davinci_mdio_x callbacks under CONFIG_PM_SLEEP to avoid build warnings.

Signed-off-by: Grygorii Strashko <Grygorii.Strashko@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>