[rfc] amdgpu/sync_file shared semaphores

[Dave Airlie]

This contains one libdrm patch and 4 kernel patches.

The goal is to implement the Vulkan KHR_external_semaphore_fd interface
for permanent semaphore behaviour for radv.

This code tries to enhance sync file to add the required behaviour
(which is mostly being able to replace the fence backing the sync file),
it also introduces new API to amdgpu to create/destroy/export/import the
sync_files which we store in an idr there, rather than fds.

There is a possibility we should share the amdgpu_sem object tracking
code for other drivers, maybe we should move that to sync_file as well,
but I'm open to suggestions for whether this is a useful approach for
other drivers.

Dave.