feat(rmmd): add support for RMM Boot interface

This patch adds the infrastructure needed to pass boot arguments from
EL3 to RMM and allocates a shared buffer between both worlds that can
be used, among others, to pass a boot manifest to RMM. The buffer is
composed a single memory page be used by a later EL3 <-> RMM interface
by all CPUs.

The RMM boot manifest is not implemented by this patch.

In addition to that, this patch also enables support for RMM when
RESET_TO_BL31 is enabled.

Signed-off-by: Javier Almansa Sobrino <javier.almansasobrino@arm.com>
Change-Id: I855cd4758ee3843eadd9fb482d70a6d18954d82a
diff --git a/changelog.yaml b/changelog.yaml
index 37a9c6d..01e91b4 100644
--- a/changelog.yaml
+++ b/changelog.yaml
@@ -563,6 +563,9 @@
           - title: TRP
             scope: trp
 
+          - title: RMMD
+            scope: rmmd
+
       - title: SPM
         scope: spm