New port: graphics/drm-next-kmod.

This port includes the current state of the FreeBSDDesktop drm-next efforts to port Linux DRM/KMS components to FreeBSD via the linuxkpi. This version of the port incorporates Linux 4.9 code and works for amdgpu (HD7000/Tahiti and newer) and i915 (HD3000/Sandy Bridge and newer) on recent FreeBSD HEAD.

A lot of people helped to make this happen by testing and reporting bugs. However, very special acknowledgements are in order for kip, markj, hselasky, kwm, Johannes Lundberg, and Pete Wright.

Reviewed by: kwm, swills (mentor), hselasky, mat, bapt, rezny, dumbbell, jbeich, markj
Approved by: kwm, swills (mentor), hselasky (earlier version), mat (earlier version)
Obtained from: https://github.com/FreeBSDDesktop/freebsd-base-graphics
Differential Revision: https://reviews.freebsd.org/D10021