Allows us to copy all the fences in a reservation object to another one.

v2: handle NULL src_list
Signed-off-by: NChristian König <christian.koenig@amd.com>
Reviewed-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1502384509-10465-2-git-send-email-alexander.deucher@amd.com