MAINTAINERS: Added device tree

Agreed between myself and Alex:
http://lists.nongnu.org/archive/html/qemu-devel/2012-06/msg03561.htmlSigned-off-by: NPeter A. G. Crosthwaite <peter.crosthwaite@petalogix.com>
Acked-by: NAlexander Graf <agraf@suse.de>
Signed-off-by: NEdgar E. Iglesias <edgar.iglesias@gmail.com>

MAINTAINERS

@@ -511,6 +511,12 @@ M: Anthony Liguori <aliguori@us.ibm.com>
 S: Maintained
 F: qemu-char.c
 
+Device Tree
+M: Peter Crosthwaite <peter.crosthwaite@petalogix.com>
+M: Alexander Graf <agraf@suse.de>
+S: Maintained
+F: device-tree.[ch]
+
 GDB stub
 M: qemu-devel@nongnu.org
 S: Odd Fixes