dt-bindings: Document devicetree binding for ARM DSU PMU

This patch documents the devicetree bindings for ARM DSU PMU.

Change-Id: Ia18788cc9340c48d3cad4d81c007d536f4e098c6
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: devicetree@vger.kernel.org
Cc: frowand.list@gmail.com
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Git-commit: 9249dee611d6624bc9044fdf3877ace67d6143ab
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>