Sub-device's power management can be provided via different ways.

Instead of hardcoding it, add a code that would be detecting it.

This uses a code similar to what's found at the atomisp driver
inside the Intel Aero repository:

	https://github.com/intel-aero/meta-intel-aero.git

(driver was removed on some commit, but it can be found on
git history).
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>