AMDGPU vs. Radeon DRM Driver Performance On Linux 4.15

For GCN 1.0 "Southern Islands" and GCN 1.1 "Sea Islands" graphics processors from AMD, they are supported both by the Radeon DRM driver (the default) as well as the AMDGPU DRM driver (designed for GCN 1.2+ GPUs). As it's been a while since comparing the performance impact of changing the kernel driver for these older GCN graphics cards, here are some fresh benchmarks using the Linux 4.15 Git kernel with Mesa 17.4-dev using a few GCN 1.0/1.1 cards.