Alias used to produce the link to the DTS API docs uses config data.
The required value in config data was being added in the wrong scope.
This moves the key addition to where the config data object is created.

DTS docs need to be placed in the same dir as main API docs.
Made DTS docs dependent on main docs and stopped separate install step
relying instead on the parent docs to install them.
This means they can no longer be build without main docs.

Added a line to sphinx python wrapper to create the destination path
if not already present.

Fixes: 7f9326423a04 ("dts: add API doc generation")

Signed-off-by: Paul Szczepanek <paul.szczepanek@arm.com>
Acked-by: Patrick Robb <probb@iol.unh.edu>