platform: intel: cavs: modify pm_notifier init for older toolchains

With Zephyr commit ae1f13149fcd ("pm: Extend pm notifier to be able to
report substate"), the pm_notifier struct was changed to include
multiple structs within a union. The xcc toolchain used for cAVS
targets cannot initialize the struct with the existing code.

Modify the code to work with the new pm.h definition and the old
compiler used.

Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>

Author: kv2019i

src/platform/intel/cavs/platform.c

@@ -107,9 +107,7 @@ int platform_boot_complete(uint32_t boot_message)
 	return 0;
 }
 
-static struct pm_notifier pm_state_notifier = {
-	.state_exit = cpu_notify_state_exit,
-};
+static struct pm_notifier pm_state_notifier;
 
 /* Runs on the primary core only */
 int platform_init(struct sof *sof)
@@ -138,6 +136,7 @@ int platform_init(struct sof *sof)
 		return ret;
 
 	/* register power states exit notifiers */
+	pm_state_notifier.state_exit = cpu_notify_state_exit;
 	pm_notifier_register(&pm_state_notifier);
 
 	/* initialize the host IPC mechanisms */