Add PoC of Arm DRTM specification version Beta-0

Change-Id: I26e6f2d4b2299edc246f5e8504d5d15b1399f640
diff --git a/docs/getting_started/build-options.rst b/docs/getting_started/build-options.rst
index 2c3cd6b..550767a 100644
--- a/docs/getting_started/build-options.rst
+++ b/docs/getting_started/build-options.rst
@@ -200,6 +200,9 @@
    that do not implement FEAT_MTPMU. For more information on FEAT_MTPMU,
    check the latest Arm ARM.
 
+-  ``DRTM_SUPPORT``: Boolean to enable support for Dynamic Root of Trust for
+   Measurement (DRTM).  Defaults to disabled.
+
 -  ``DYN_DISABLE_AUTH``: Provides the capability to dynamically disable Trusted
    Board Boot authentication at runtime. This option is meant to be enabled only
    for development platforms. ``TRUSTED_BOARD_BOOT`` flag must be set if this