lib: os: poweroff: Disable ZLIs before poweroff

We currently only disable "normal" IRQs with irq_lock(). This is not
sufficient if ZLIs are enabled, as even though they are supposed to
be "above" the kernel, they must not interrupt the poweroff procedure.

Signed-off-by: Bjarki Arge Andreasen <bjarki.andreasen@nordicsemi.no>

lib/os/poweroff.c

@@ -10,5 +10,9 @@ void sys_poweroff(void)
 {
 	(void)irq_lock();
 
+#if defined(CONFIG_ZERO_LATENCY_IRQS)
+	(void)arch_zli_lock();
+#endif /* CONFIG_ZERO_LATENCY_IRQS */
+
 	z_sys_poweroff();
 }