MAINTAINERS: dt: fix pointers for ARM Integrator, Versatile and RealView

There's a conversion from a plain text binding file into 4 yaml ones.
The old file got removed, causing this new warning:

	Warning: MAINTAINERS references a file that doesn't exist: Documentation/devicetree/bindings/arm/arm-boards

Address it by replacing the old reference by the new ones

Fixes: 4b900070 ("dt-bindings: arm: Add Versatile YAML schema")
Fixes: 2d483550 ("dt-bindings: arm: Drop the non-YAML bindings")
Fixes: 7db625b9 ("dt-bindings: arm: Add RealView YAML schema")
Fixes: 4fb00d90 ("dt-bindings: arm: Add Versatile Express and Juno YAML schema")
Fixes: 33fbfb3e

 ("dt-bindings: arm: Add Integrator YAML schema")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>