MAINTAINERS: Add me and Bertrand as device tree maintainers

With Arm port being the major recipient of dt related patches and the
future need of incorporating dt support into other ports, we'd like to
keep an eye on these changes.

Signed-off-by: Michal Orzel <michal.orzel@amd.com>
Acked-by: Bertrand Marquis <bertrand.marquis@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>

MAINTAINERS

@@ -287,6 +287,8 @@ F:	automation/
 DEVICE TREE
 M:	Stefano Stabellini <sstabellini@kernel.org>
 M:	Julien Grall <julien@xen.org>
+M:	Bertrand Marquis <bertrand.marquis@arm.com>
+M:	Michal Orzel <michal.orzel@amd.com>
 S:	Supported
 F:	xen/common/libfdt/
 F:	xen/common/device_tree.c