MAINTAINERS: Add documentation and dt-bindings for exynos stuff

Extend the Samsung Exynos maintainer entry to match SoC documentation
and SoC dt-bindings directories. Without that some files, like
bindings/arm/samsung/pmu.txt, are not matched by existing patterns.

This also may serve as a hint where new documentation and bindings
(not matching specific subsystem) should be put.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Kukjin Kim <kgene@kernel.org>

MAINTAINERS

@@ -1439,6 +1439,10 @@ F:	drivers/*/*s3c2410*
 F:	drivers/*/*/*s3c2410*
 F:	drivers/spi/spi-s3c*
 F:	sound/soc/samsung/*
+F:	Documentation/arm/Samsung/
+F:	Documentation/devicetree/bindings/arm/samsung/
+F:	Documentation/devicetree/bindings/sram/samsung-sram.txt
+F:	Documentation/devicetree/bindings/power/pd-samsung.txt
 N:	exynos
 
 ARM/SAMSUNG MOBILE MACHINE SUPPORT