struct isst_id contains cpu, package and die info, and it can represent
a specific SST power domain.

Introduce is_cpu_in_power_domain() helper to identify if a cpu is in a
specified power_domain.

And cleanup the code to use the new helper.
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>