soc: intel_adsp/ace: use functions to do CPU power control

Instead of relying on direct memory access via structs to
control CPU power and status, using inline functions instead
to hide the details. This makes reading the common code a bit
cleaner.

The function names are generic and not architecture or
platform specific, in an attempt to ease future arch or
platform additions with code reuse. Or else we would need to
rename these.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>