PM: Revert "driver core: platform_bus: allow runtime override of dev_pm_ops"

The platform_bus_set_pm_ops() operation is deprecated in favor of the
new device power domain infrastructre implemented in commit
7538e3db6e015e890825fbd9f8659952896ddd5b (PM: add support for device
power domains)

Signed-off-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>