Extend messaging methods field to include managed exit support

As per FF-A v1.0 spec, Table 3.1, messaging method field also contains
information about whether partition supports managed exit or not.
Since a partition can support managed exit only if it supports direct
messaging, there are two new possible values, managed exit with only
direct messaging or with both messaging methods.

This patch also adds "managed exit" support field in vm structure.

Change-Id: I0d6612f523f762581fc0d01ea3db9ebc325ffab9
Signed-off-by: Manish Pandey <manish.pandey2@arm.com>
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
diff --git a/src/manifest_test.cc b/src/manifest_test.cc
index 1571b79..5f85fca 100644
--- a/src/manifest_test.cc
+++ b/src/manifest_test.cc
@@ -818,7 +818,7 @@
 		.Property("entrypoint-offset", "<0x00001000>")
 		.Property("xlat-granule", "<0>")
 		.Property("boot-order", "<0>")
-		.Property("messaging-method", "<3>")
+		.Property("messaging-method", "<5>")
 		.Build();
 	/* clang-format on */
 	ASSERT_EQ(ffa_manifest_from_vec(&m, dtb),