VideoCommon: Make GPU syncing hack optional

This hack is there for quite a long time, and lots of games crashes if it's disabled.
But it's still a hack, so it shouldn't be enabled hard coded. This commit create a new
ini option for this hack which is enabled by default.
Maybe some games does still run very fine without this hack.
Merge pull request #1745 from degasus/remove_gpu_sync

VideoCommon: Make GPU syncing hack optional