stm class: p_sys-t: Add support for CLOCKSYNC packets

This adds support for CLOCKSYNC SyS-T packets, that establish correlation
between the transport clock (STP timestamps) and SyS-T timestamps. These
packets are sent periodically to allow the decoder to keep both time
sources in sync.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Tested-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>