PTP: add support for one-shot output

Some controllers allow for a one-shot output pulse, in contrast to
periodic output. Now that we have extensible versions of our IOCTLs, we
can finally make use of the 'flags' field to pass a bit telling driver
that if we want one-shot pulse output.

Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Reviewed-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>