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.
GeometryShaderManager: Set viewport in SetConstants().

Setting it in the callback is too early.
Merge pull request #1771 from Armada651/geom-viewport

GeometryShaderManager: Set viewport in SetConstants().
Merge pull request #1745 from degasus/remove_gpu_sync

VideoCommon: Make GPU syncing hack optional
Merge branch 'master' of https://github.com/dolphin-emu/dolphin into VR-Hydra

Conflicts:
	Source/Core/VideoCommon/GeometryShaderManager.cpp