drm/msm/sde: extend frame retire event handling

Simplify retire event by avoiding special handling and extend
frame event to identify the connector or encoder firing the
frame event. As crtc can be really driving multiple connectors
whose frame events are not same or synchronized, this isolation
of events per connector is required to handle fences.

Change-Id: I2e82ae2288da4206afa197749aa57a2621b4d3f7
Signed-off-by: Prabhanjan Kandula <pkandula@codeaurora.org>