sync_file: Return consistent status in SYNC_IOC_FILE_INFO

sync_file_ioctl_fence_info has a race between filling the status
of the underlying fences and the overall status of the sync_file.
If fence transitions in the time frame between its sync_fill_fence_info
and the later dma_fence_is_signaled for the sync_file, the returned
information is inconsistent showing non-signaled underlying fences but
an overall signaled state.

This patch changes sync_file_ioctl_fence_info to track what has been
encoded and using that as the overall sync_file status.

Tested-by: Vamsidhar Reddy Gaddam <vamsidhar.gaddam@arm.com>
Signed-off-by: John Einar Reitan <john.reitan@arm.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171009134936.27219-1-john.reitan@arm.com