dt-bindings: arm: Drop the non-YAML bindings

We created new bindings for the ARM Board using YAML
so delete the old human-parseable-only bindings.

Cc: Sudeep Holla <sudeep.holla@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>