Implement finding the right timeline point in drm_syncobj_find_fence.

v2: return -EINVAL when the point is not submitted yet.
v3: fix reference counting bug, add flags handling as well
v4: add timeout for find fence

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Link: https://patchwork.freedesktop.org/patch/295786/?series=58813&rev=1