layers: Remove wrapping of GPU objects by loader and layers

layers: Remove wrapping of GPU objects by loader and layers

Loader only wraps GPU objects for creating a layer chain. After layer activation
layers and loader use unwrapped gpu object returned by the driver.

This is a large simplification.

This fixes a nasty bug where layers intercepting entrypoints with gpu objects
but not all these entrypoints would fail.  These would cause non-uniform
unwrapping of gpu objects by the time the driver was called with a gpu object.

Fixes issue in loader_get_icd where it was trying to compare a wrapped GPU
against a non-wrapped GPU.