MAINTAINERS: Add myself as reviewer of 'Machine core' API

In order to help Eduardo and Marcel with the machine
core API, add myself as reviewer. That will also help
me to learn more about this subsystem :)

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed by: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
Message-Id: <20211007093108.323223-1-philmd@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

MAINTAINERS

@@ -1617,6 +1617,7 @@ F: pc-bios/bios-microvm.bin
 Machine core
 M: Eduardo Habkost <ehabkost@redhat.com>
 M: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
+R: Philippe Mathieu-Daudé <philmd@redhat.com>
 S: Supported
 F: cpu.c
 F: hw/core/cpu.c