Add TRNG Firmware Interface service

This adds the TRNG Firmware Interface Service to the standard
service dispatcher. This includes a method for dispatching entropy
requests to platforms and includes an entropy pool implementation to
avoid dropping any entropy requested from the platform.

Change-Id: I71cadb3cb377a507652eca9e0d68714c973026e9
Signed-off-by: Jimmy Brisson <jimmy.brisson@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/docs/glossary.rst b/docs/glossary.rst
index 08add3a..54820e4 100644
--- a/docs/glossary.rst
+++ b/docs/glossary.rst
@@ -193,6 +193,9 @@
    TLK
       Trusted Little Kernel. A Trusted OS from NVIDIA.
 
+   TRNG
+      True Randon Number Generator (hardware based)
+
    TSP
       Test Secure Payload