drm: remove writeq/readq function definitions

Instead of rewriting write/readq, use linux/io-64-nonatomic-lo-hi.h which
already have them.

Signed-off-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170602112510.17544-1-clabbe.montjoie@gmail.com