Blender Git Loki

Cycles X: restore baking of more passes

The idea is to map baking settings to render passes. Still various passes
missing. In particular AO and Shadow (also missing for regular render) and
the complete filter options for light baking.

Some details of the implementation:
* The pass accessor can now read e.g. roughness into an RGBA image, which
is convenient for baking.
* ShaderEvalType is now only used for displace/background baking, no longer
part of the kernel and much smaller. Instead passes are used.
* Roughness render pass added for baking.
* Normals are baked as -1..1 just like the render pass, the Blender side
was updated since it expected 0..1 previously.

Differential Revision: https://developer.blender.org/D11534