Add myself as maintainer for TPM code

Also add backends/tpm.c to the list of files.

Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Acked-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

MAINTAINERS

@@ -1535,12 +1535,14 @@ F: docs/devel/tracing.txt
 T: git git://github.com/stefanha/qemu.git tracing
 
 TPM
-S: Orphan
+M: Stefan Berger <stefanb@linux.vnet.ibm.com>
+S: Maintained
 F: tpm.c
 F: hw/tpm/*
 F: include/hw/acpi/tpm.h
 F: include/sysemu/tpm*
 F: qapi/tpm.json
+F: backends/tpm.c
 
 Checkpatch
 S: Odd Fixes