drm / drm2 removal in 12

[Matthew Macy]

Just in case anyone misses the change to UPDATING:

20180821:
        drm and drm2 have been removed. Users on powerpc, 32-bit hardware,
        or with GPUs predating Radeon and i915 will need to install the
        graphics/drm-legacy-kmod. All other users should be able to use
        one of the LinuxKPI-based ports: graphics/drm-stable-kmod,
        graphics/drm-next-kmod, graphics/drm-devel-kmod.

Note that this applies only to 12.

-M