feat(interrupts): preferred managed exit signal

A SP optionally specifies if vIRQ is the preferred choice for
signaling Managed Exit in response to a non secure interrupt.

Moreover, SPMC enables the following virtual maintenenace interrupts
by default for each Secure Partition:
  > Managed Exit Interrupt
  > Notification Pending Interrupt

Change-Id: I17131b42ee6fae2896804e4f952d9a371f237cd5
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
diff --git a/src/manifest.c b/src/manifest.c
index b6c6e9a..90aefd7 100644
--- a/src/manifest.c
+++ b/src/manifest.c
@@ -910,6 +910,12 @@
 				"partition\n");
 			return MANIFEST_ILLEGAL_NS_ACTION;
 		}
+
+		TRY(read_bool(&root, "managed-exit-virq",
+			      &vm->partition.me_signal_virq));
+		if (vm->partition.me_signal_virq) {
+			dlog_verbose("  Managed Exit signaled through vIRQ\n");
+		}
 	}
 
 	TRY(read_bool(&root, "notification-support",