drm: Make uapi headers C89 pendantic compliant

This ports the below libdrm commit to the kernel

commit 0f4452bb51306024fbf4cbf77d8baab20cefba67
Author: Daniel Kurtz <djkurtz@chromium.org>
Date:   Mon Aug 26 23:39:16 2013 +0800

    libdrm: Make some drm headers compatible with gcc -std=c89 -pedantic

    The following minor changes were needed to these headers:
     * Convert // comments to /* */
     * No , after final member of enum

    With these changes, these header files can be included by a program that
    is built with gcc options:
      -std=c89 -Werror -pedantic

    Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
    Signed-off-by: Eric Anholt <eric@anholt.net>
    Reviewed-by: Eric Anholt <eric@anholt.net>

Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1459348943-12803-2-git-send-email-daniel.vetter@ffwll.ch