BoardConfig: Add and document vsync phase offset setting
BoardConfig: Add and document vsync phase offset setting

Bug: 10624956
Change-Id: I82def5730f9d09396809d4b8cd2ea44829b21f22

xorware/android_build,xorware/android_build,xorware/android_build,xorware/android_build,xorware/android_build