Documentation: bindings: decouple juno specific details from generic binding

Since SCPI is a generic protocol and the bindings are intended to be
generic, we need to decouple all the platform specific binding details
out of the generic bindings.

This patch moves are the Juno platform specific details into a separate
binding document.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>