Don't lookup a depth buffer if depth test is always pass without write
Boost performance on Tekken5 when depth emulation is enabled in openGL
(Tekken5 sets same address for both the RT and the depth but depth is disabled)
v2:
Keep ds if DATE is enabled (some implementation uses a stencil buffer)
Be more aggressive to avoid an useless depth lookup
Gregory Hainaut
1853d0d16d