anv: Fix near plane clipping on Gen7/7.5.

anv: Fix near plane clipping on Gen7/7.5.

The Gen7/7.5 clip code used APIMODE_OGL, while the Gen8+ clip code used
APIMODE_D3D.  The meaning hasn't changed, so one of these must be wrong.

It appears that the hardware documentation is completely wrong.  It
claims that the "API Mode" bit means:

   0h    APIMODE_OGL    NEAR_VP boundary == 0.0 (NDC)
   1h    APIMODE_D3D    NEAR_VP boundary == -1.0 (NDC)

However, DirectX typically uses 0.0 for the near plane, while unextended
OpenGL uses -1.0.  i965's gen6_clip_state.c uses APIMODE_D3D for the
GL_ZERO_TO_ONE case, so I believe the meanings are backwards from what
the documentation says.

Section 23.2 ("Primitive Clipping") of the Vulkan 1.0.21 specification
contains the following equations:

   -w_c <= x_c <= w_c
   -w_c <= y_c <= w_c
      0 <= z_c <= w_c

This means that Vulkan follows D3D semantics.

Cc: "12.0" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>