MAINTAINERS: add dt binding headers to memory controller drivers entry

Cover also the include/dt-bindings/memory/ headers in the memory
controller drivers entry.
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20201002155713.3569-1-krzk@kernel.org

MAINTAINERS

@@ -11332,6 +11332,7 @@ S:	Maintained
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/krzk/linux-mem-ctrl.git
 F:	Documentation/devicetree/bindings/memory-controllers/
 F:	drivers/memory/
+F:	include/dt-bindings/memory/
 
 MEMORY FREQUENCY SCALING DRIVERS FOR NVIDIA TEGRA
 M:	Dmitry Osipenko <digetx@gmail.com>