clients: rename simple-dmabuf into simple-dmabuf-intel

clients: rename simple-dmabuf into simple-dmabuf-intel

This client was using an Intel-specific way to allocate a dmabuf, so it
makes sense to have that in its name.

Signed-off-by: Emmanuel Gil Peyrot <emmanuel.peyrot@collabora.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Derek Foreman <derekf@osg.samsung.com>
Differential Revision: https://phabricator.freedesktop.org/D342