Fixes for Cycles source reorganize

Cycles: remove prefix from source code file names

Remove prefix of filenames that is the same as the folder name. This used
to help when #includes were using individual files, but now they are always
relative to the cycles root directory and so the prefixes are redundant.

For patches and branches, git merge and rebase should be able to detect the
renames and move over code to the right file.

Cycles: changes to source code folders structure

* Split render/ into scene/ and session/. The scene/ folder now contains the
scene and its nodes. The session/ folder contains the render session and
associated data structures like drivers and render buffers.
* Move top level kernel headers into new folders kernel/camera/, kernel/film/,
kernel/light/, kernel/sample/, kernel/util/
* Move integrator related kernel headers into kernel/integrator/
* Move OSL shaders from kernel/shaders/ to kernel/osl/shaders/

For patches and branches, git merge and rebase should be able to detect the
renames and move over code to the right file.

Fix Cycles HIP binaries always recompiling

Fix Cycles HIP binaries always recompiling

This part should not have been copied from CUDA.

Cycles: eliminate HIP architectures that fail to build

Cleanup: refactor float/half conversions for clarity

Cycles: test building for many HIP architectures

Most of these will likely not work, but let's see what happens.

Cycles: more HIP binaries testing

Cycles: more HIP binaries testing