doc: Format security advisory titles and headings

Required so that the advisory documents are all valid RST files (with a
header) and that they all integrate into the document tree.

Change-Id: I68ca2b0b9e648e24b460deb772c471a38518da26
Signed-off-by: Paul Beesley <paul.beesley@arm.com>
diff --git a/docs/security_advisories/security-advisory-tfv-5.rst b/docs/security_advisories/security-advisory-tfv-5.rst
index 4479bf0..2214f2d 100644
--- a/docs/security_advisories/security-advisory-tfv-5.rst
+++ b/docs/security_advisories/security-advisory-tfv-5.rst
@@ -1,3 +1,6 @@
+Advisory TFV-5 (CVE-2017-15031)
+===============================
+
 +----------------+-------------------------------------------------------------+
 | Title          | Not initializing or saving/restoring ``PMCR_EL0`` can leak  |
 |                | secure world timing information                             |