drivers: video: fix vsync on p970

hub uses DSI Command Mode Manual Update Panel and the refresh rate
of the panel depends upon the userspace. Due to this, the VSYNC is
slower which causes the vsync timeouts in the userspace.

Instead of sending the vsync after the framedone, we use the panel
vsync irq to send the vsync, which works better.

This patch requires changes to the hwc.

Change-Id: Ief4bd6741993eebbdda00bdc27576117d641d6d0