kernel: add z_fatal_halt() to interface

Intended to be called from application-level implementations
of k_sys_fatal_error_handler().

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>

include/fatal.h

@@ -31,6 +31,16 @@ enum k_fatal_error_reason {
 	 */
 };
 
+/**
+ * @brief Halt the system on a fatal error
+ *
+ * Invokes architecture-specific code to power off or halt the system in
+ * a low power state. Lacking that, lock interupts and sit in an idle loop.
+ *
+ * @param reason Fatal exception reason code
+ */
+FUNC_NORETURN void k_fatal_halt(unsigned int reason);
+
 /**
  * @brief Fatal error policy handler
  *