qemu: Implement PSCI_CPU_OFF.

This is based on the rpi implementation from
https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/2746.

Signed-off-by: Andrew Walbran <qwandor@google.com>
Change-Id: I5fe324fcd9d5e232091e01267ea12147c46bc9c1
diff --git a/lib/psci/psci_common.c b/lib/psci/psci_common.c
index ea1a01d..5ab15c6 100644
--- a/lib/psci/psci_common.c
+++ b/lib/psci/psci_common.c
@@ -775,7 +775,7 @@
 	 * suspend.
 	 */
 	if (psci_get_aff_info_state() == AFF_STATE_OFF) {
-		ERROR("Unexpected affinity info state");
+		ERROR("Unexpected affinity info state.\n");
 		panic();
 	}