Pull in drm 5.1

[amshafer]

This imports drm code up to linux 5.1. Tested on i915 (haswell, modern) and amdgpu. More testing is always welcome.

Most of the work was done by @myfreeweb, and linuxkpi bits were merged by @hselasky in the following review: https://reviews.freebsd.org/D24611

This requires CURRENT later than r360622

[olegsidorkin]

Tested with vega20 (KDE, glxgears, glmark2) - loads and works without any articfacts. Thanks.

[jbeich]

No regressions on Skylake. Tested for 3 days:

• Sway/wlroots (1.4/0.10, master)
• Mesa (19.0.8/master, iris, i965)
• mpv (EGL, Vulkan, VAAPI)
• Firefox (WebRender, VAAPI)
• rpcs3/yuzu/ppsspp (OpenGL, Vulkan)
• libva-intel-media-driver (H264, VC1)
• libva-intel-driver (VP9 hybrid)
• intel-compute-runtime (OCL, L0)
• intel-media-sdk (H264 lookahead)
• xf86-video-intel (SNA+DRI3)
• compat.linuxkpi.i915_enable_guc=-1

[valpackett]

This should probably be closed now that 5.2-5.3 are in https://github.com/freebsd/drm-kmod :)