Tests: add CMake option to run Cycles regression tests on GPU devices

CYCLES_TEST_DEVICES is a list of devices (CPU, CUDA, OPTIX, OPENCL). It is set
to CPU only by default.

Test output is now writen to build/tests/cycles/<device>, and the HTML report
has separate report pages for the different devices, with option to compare
between CPU and GPU renders.

Various GPU tests are still failing due to CPU/GPU differences, these are to be
fixed or blacklisted still.

Ref T82193

tests/python/workbench_render_tests.py

@@ -72,7 +72,7 @@ def main():
     report = render_report.Report("Workbench", output_dir, idiff)
     report.set_pixelated(True)
     report.set_reference_dir("workbench_renders")
-    report.set_compare_engines('workbench', 'eevee')
+    report.set_compare_engine('eevee')
     ok = report.run(test_dir, blender, get_arguments, batch=True)
 
     sys.exit(not ok)