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: 2d483550b6d2 ("dt-bindings: arm: Drop the non-YAML bindings")
Fixes: 33fbfb3eaf4e ("dt-bindings: arm: Add Integrator YAML schema")
Fixes: 4b900070d50d ("dt-bindings: arm: Add Versatile YAML schema")
Fixes: 7db625b9fa75 ("dt-bindings: arm: Add RealView YAML schema")
Fixes: 4fb00d9066c1 ("dt-bindings: arm: Add Versatile Express and Juno YAML schema")
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>
Link: https://lore.kernel.org/r/eae344[e-mail]
Signed-off-by: Jonathan Corbet <[e-mail]>

MAINTAINERS

···
 M:	Linus Walleij <[e-mail]>
 L:	[e-mail] (moderated for non-subscribers)
 S:	Maintained
-F:	Documentation/devicetree/bindings/arm/arm-boards
+F:	Documentation/devicetree/bindings/arm/arm,integrator.yaml
+F:	Documentation/devicetree/bindings/arm/arm,realview.yaml
+F:	Documentation/devicetree/bindings/arm/arm,versatile.yaml
+F:	Documentation/devicetree/bindings/arm/arm,vexpress-juno.yaml
 F:	Documentation/devicetree/bindings/auxdisplay/arm-charlcd.txt
 F:	Documentation/devicetree/bindings/clock/arm,syscon-icst.yaml
 F:	Documentation/devicetree/bindings/i2c/i2c-versatile.txt