drm: helper macros to print composite types

I'll want to print things in a similar way in a later patch.  This will
make it easier.

Signed-off-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1478358492-30738-2-git-send-email-robdclark@gmail.com