Bug 1043822 - Support SW Vsync Timer

Use nanosleep to implement SW Vsync Timer
Bug 987527 - Register Vsync monitor to HWComposer

In order to enable/disable the Vsync from mHwc, we should make sure
the order of each command is correct. In this patch, I added an
interface for registering these mHwc callback functions and some
accessor/helper functions for manipulating Hwc Vsync.
Bug 1048667 - Part1: silk preference
vsync protocol and dispatch framework
implement GonkVsyncDispatcher
enable silk
rename StartUp -> startup, ShutDown->Shutdown.
fix if-else indent.
hide nullptr at VsyncDispatcher.h
Bug 987529 - integrate refresh driver into vsync dispatcher
add software vsync timer support