power_mgmt: Enhances the DEVICE_INIT_PM macros

Enhances the DEVICE_INIT_PM and SYS_INIT_PM macros so the drivers
can avoid #ifdef checks in C code.  This also prepares for future
merging of the different versions of these macros.

Change-Id: I2cc50686a2e2c6bdf675bff8b208f741231c2537
Signed-off-by: Ramesh Thomas <ramesh.thomas@intel.com>