doc: secure partition manager design

Former EL3 Secure Partition Manager using MM protocol is renamed
Secure Partition Manager (MM).
A new Secure Partition Manager document covers TF-A support for the
PSA FF-A compliant implementation.

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: I9763359c2e96181e1726c8ad72738de293b80eb4
diff --git a/docs/components/index.rst b/docs/components/index.rst
index 18b1e38..861a85d 100644
--- a/docs/components/index.rst
+++ b/docs/components/index.rst
@@ -16,7 +16,8 @@
    ras
    romlib-design
    sdei
-   secure-partition-manager-design
+   secure-partition-manager
+   secure-partition-manager-mm
    psa-ffa-manifest-binding
    xlat-tables-lib-v2-design
    cot-binding