i2c: Encourage move to dev_pm_ops by warning on use of legacy methods

Since the PM core wishes to transition away from the legacy suspend
and resume methods and since removing them makes using PM core features
like runtime PM much easier start warning when a driver is registered
using the legacy methods.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>