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/inc/hf/manifest.h b/inc/hf/manifest.h
index 0985217..60c6f76 100644
--- a/inc/hf/manifest.h
+++ b/inc/hf/manifest.h
@@ -151,6 +151,8 @@
 	uint8_t messaging_method;
 	/** mandatory - action in response to non secure interrupt */
 	uint8_t ns_interrupts_action;
+	/** optional - managed exit signaled through vIRQ */
+	bool me_signal_virq;
 	/** optional - receipt of notifications. */
 	bool notification_support;
 	/** optional */