MAINTAINERS: add entry for "Unimplemented" device

Also voluntary myself as reviewer
Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20170629150308.22766-6-f4bug@amsat.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

MAINTAINERS

@@ -1155,6 +1155,13 @@ F: docs/specs/vmgenid.txt
 F: tests/vmgenid-test.c
 F: stubs/vmgenid.c
 
+Unimplemented device
+M: Peter Maydell <peter.maydell@linaro.org>
+R: Philippe Mathieu-Daudé <f4bug@amsat.org>
+S: Maintained
+F: include/hw/misc/unimp.h
+F: hw/misc/unimp.c
+
 Subsystems
 ----------
 Audio