loader: Implement new layer initialization

We now call down the instance and device chains
as part of the creation process. The loader puts
together "LinkInfo" structures that each layer
uses to reference the next layer down in the stack.
These info structures are attached to the CreateInfo
pNext structure. Also have an info structure that
the loader terminator functions (CreateInstance_Bottom
and CreateDevice_Bottom) that includes loader state
they need.
As part of this the CreateDevice function now lives
on the device chain and it has been split into
Top and Bottom functions. Top builds the LinkInfo
structures and Bottom makes the actual call to the ICD
to create the device object.

Change-Id: I5f5a6d579c34942511cce288ba8fa51f9f89f67f