[RFC] DRM synchronisation objects

[Dave Airlie]

This series enhances my previous semaphore work on for amdgpu,
with a generic DRM sync object. (drm_syncobj).

It first enhances sync_file to have a type/flags so we can have
different semantics for different sync files, and a wait
to retrieve the type of sync_file for userspace.

Then it adds drm sync objects which are just a drm wrapper around
a sync_file object, allowing creation/info/destroy and import/export
of the objects.

Next it enhances sync_file to have semaphore semantics for Vulkan.

Finally it adds amdgpu support to it's command submission paths to
use the new code.

I've hopefully fixed up the things pointed out in the last 
review of the sync_file fence changes, I do wonder if we should
just block poll on semaphore objects as currently I've no use
case for this.

Dave.