DSU: Implement workaround for errata 798953

Under certain near idle conditions, DSU may miss response transfers on
the ACE master or Peripheral port, leading to deadlock. This workaround
disables high-level clock gating of the DSU to prevent this.

Change-Id: I820911d61570bacb38dd325b3519bc8d12caa14b
Signed-off-by: Louis Mayencourt <louis.mayencourt@arm.com>
diff --git a/docs/cpu-specific-build-macros.rst b/docs/cpu-specific-build-macros.rst
index 0b58169..7b7f4cd 100644
--- a/docs/cpu-specific-build-macros.rst
+++ b/docs/cpu-specific-build-macros.rst
@@ -233,6 +233,11 @@
 
 For DSU errata, the following build flags are defined:
 
+-  ``ERRATA_DSU_798953``: This applies errata 798953 workaround for the
+   affected DSU configurations. This errata applies only for those DSUs that
+   revision is r0p0 (on r0p1 it is fixed). However, please note that this
+   workaround results in increased DSU power consumption on idle.
+
 -  ``ERRATA_DSU_936184``: This applies errata 936184 workaround for the
    affected DSU configurations. This errata applies only for those DSUs that
    contain the ACP interface **and** the DSU revision is older than r2p0 (on