drm/amd/sched: add a unique job id to amd_sched_job

A unique id is useful for debugging and tracing. Intended to replace
pointers in ftrace output.

Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Andres Rodriguez <andresx7@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>