Correct a LOR issue on FreeBSD by allocating temporary space and doing a

    single DRM_COPY_FROM_USER rather than DRM_VERIFYAREA_READ followed by
    tons of DRM_COPY_FROM_USER_UNCHECKED. I don't like the look of the
    temporary space allocation, but I like the simplification in the rest
    of the file. Tested with glxgears, tuxracer, and q3 on a savage4.