anv: Stop setting 3DSTATE_PS_EXTRA::PixelShaderHasUAV

We've had several broadwell hangs that have come down to this bit just
not working correctly.  Most recently, we've had a pile of hangs
reported with apps running under DXVK:

https://github.com/doitsujin/dxvk/issues/469



Instead, use the bit that doesn't try to imply weird D3D coherency
things and just force-enables the PS like we want.

cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
(cherry picked from commit abd629eb)