drm/amdkfd: Add metadata ring buffer for compute

drm/amdkfd: Add metadata ring buffer for compute

Add support for separate ring-buffer for metadata packets when using
compute queues. Userspace application allocate the metadata ring-buffer
and the queue ring-buffer with a single allocation. The metadata
ring-buffer starts after the queue ring-buffer.

Signed-off-by: David Yat Sin <David.YatSin@amd.com>
Reviewed-by: Philip Yang <Philip.Yang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>