MAINTAINERS: arm64: Remove boot/dts/ directory from arm64 entry

The arm-soc tree does a good job handling .dts files, so exclude them
from the ARM64 entry in MAINTAINERS.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: NOlof Johansson <olof@lixom.net>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

MAINTAINERS

@@ -2264,6 +2264,7 @@ L:	linux-arm-kernel@lists.infradead.org (moderated for non-subscribers)
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git
 S:	Maintained
 F:	arch/arm64/
+X:	arch/arm64/boot/dts/
 F:	Documentation/arm64/
 
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