Fix "shutdown -r" and "shutdown -h"

- "shutdown -r" will reset the system
- "shutdown -h" will power off the system
We don't drop into OFW as newer versions of solaris don't do this either

sys/sun4v/sun4v/machdep.c

@@ -717,7 +717,7 @@ cpu_shutdown(void *args)
 #ifdef SMP
 	cpu_mp_shutdown();
 #endif
-	OF_exit();
+	hv_mach_exit(0);
 }
 
 /* Get current clock frequency for the given cpu id. */

sys/sun4v/sun4v/mp_machdep.c

@@ -448,7 +448,6 @@ cpu_ipi_stop(struct trapframe *tf)
 	while ((started_cpus & PCPU_GET(cpumask)) == 0) {
 		if ((shutdown_cpus & PCPU_GET(cpumask)) != 0) {
 			atomic_clear_int(&shutdown_cpus, PCPU_GET(cpumask));
-			OF_exit();
 		}
 	}
 	atomic_clear_rel_int(&started_cpus, PCPU_GET(cpumask));

sys/sun4v/sun4v/vm_machdep.c

@@ -321,10 +321,7 @@ cpu_reset(void)
 			bspec[0] = '\0';
 		bspec[sizeof(bspec) - 1] = '\0';
 	}
-#ifdef notyet
-	/* XXX SUN4V_FIXME */
-	openfirmware_exit(&args);
-#endif
+	hv_mach_sir();
 }
 
 /*