[Why&How]
The driver always wants to synchronize streams
to the first edge of master's vsync pulse.
In order to determine that we can read timing
flags that are used to program vsync.

Master stream's vsync polarity - Multi Display Stream Synchronization edge:

        Negative               -              Falling Edge

        Positive               -              Rising Edge
Signed-off-by: NMikita Lipski <mikita.lipski@amd.com>
Reviewed-by: NSun peng Li <Sunpeng.Li@amd.com>
Acked-by: NQingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>