pm: policy: fix mocks of CONFIG_PM_POLICY_DEVICE_CONSTRAINTS

The APIs pm_policy_device_power_lock_get and
pm_policy_device_power_lock_put are not mocked properly as they
should be excluded based on CONFIG_PM_POLICY_DEVICE_CONSTRAINTS,
not CONFIG_PM.

Signed-off-by: Bjarki Arge Andreasen <bjarki.andreasen@nordicsemi.no>