docs(maintainers): add missing files related to SPMD

Few header files are added to the list maintained by SPMD code owners.
Also, added myself as one of the code owners for SPMD module in TF-A.

Change-Id: Ic017cb98013d349702c35837463586d4aae65543
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
diff --git a/docs/about/maintainers.rst b/docs/about/maintainers.rst
index 1dda0ff..ddcb7e6 100644
--- a/docs/about/maintainers.rst
+++ b/docs/about/maintainers.rst
@@ -123,7 +123,13 @@
 :|G|: `odeprez`_
 :|M|: Joao Alves <Joao.Alves@arm.com>
 :|G|: `J-Alves`_
+:|M|: Madhukar Pappireddy <Madhukar.Pappireddy@arm.com>
+:|G|: `madhukar-Arm`_
 :|F|: services/std_svc/spmd/\*
+:|F|: plat/common/plat_spmd_manifest.c
+:|F|: include/services/ffa_svc.h
+:|F|: include/services/el3_spmd_logical_sp.h
+:|F|: include/services/spmd_svc.h
 
 Exception Handling Framework (EHF)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^