arm: Add arch/arm/dts/Makefile specifically to MAINTAINERS

In order to reduce the number of people that are cc'd on a patch for
simply touching arch/arm/dts/Makefile (which is a big common file) add
an entry specifically to MAINTAINERS under the ARM entry.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/MAINTAINERS b/MAINTAINERS
index 523c17e..8b60db4 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -132,6 +132,7 @@
 S:	Maintained
 T:	git https://source.denx.de/u-boot/custodians/u-boot-arm.git
 F:	arch/arm/
+F:	arch/arm/dts/Makefile
 F:	cmd/arm/
 
 ARM ALTERA SOCFPGA