Documentation: devicetree: fix reference to legacy wakeup properties

This patch marks all the reference to the legacy wakeup bindings
and replaces them with the standard "wakeup-source" property.

All these legacy property are also listed under a separate section in
the generic wakeup-source binding document.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Rob Herring <robh@kernel.org>