MAINTAINERS: Add Kumar to Device Tree Binding maintainers group

I'm tossing my hat into the ring of maintainers/reviewers for device tree
bindings based on history of dealing with DT on embedded PPC and starting
work on ARM SoCs.

Signed-off-by: Kumar Gala <[e-mail]>
Acked-by: Pawel Moll <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Acked-by: Stephen Warren <[e-mail]>
Cc: Ian Campbell <[e-mail]>
Cc: Rob Herring <[e-mail]>
Cc: Grant Likely <[e-mail]>
Cc: Olof Johansson <[e-mail]>
Signed-off-by: Rob Herring <[e-mail]>

MAINTAINERS

···
 M:	Mark Rutland <[e-mail]>
 M:	Stephen Warren <[e-mail]>
 M:	Ian Campbell <[e-mail]>
+M:	Kumar Gala <[e-mail]>
 L:	[e-mail]
 S:	Maintained
 F:	Documentation/devicetree/