Introduce isst_is_punit_valid() for checking a valid domain.

For current platforms, it requires a punit 0 in a valid Package/Die.

No functional changes are expected.
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
[srinivas.pandruvada@linux.intel.com: changelog edits]
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>