anv/gen7_pipeline: Set PixelShaderKillPixel for discards

According to the IVB PRM Vol2 P1, this bit must be set if a pixel shader
contains a discard instruction.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97207
Cc: "12.0" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Nanley Chery <nanley.g.chery@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/intel/vulkan/gen7_pipeline.c

@@ -298,6 +298,7 @@ genX(graphics_pipeline_create)(
          wm.LineEndCapAntialiasingRegionWidth   = 0; /* 0.5 pixels */
          wm.LineAntialiasingRegionWidth         = 1; /* 1.0 pixels */
          wm.PointRasterizationRule              = RASTRULE_UPPER_RIGHT;
+         wm.PixelShaderKillPixel                = wm_prog_data->uses_kill;
          wm.PixelShaderComputedDepthMode        = wm_prog_data->computed_depth_mode;
          wm.PixelShaderUsesSourceDepth          = wm_prog_data->uses_src_depth;
          wm.PixelShaderUsesSourceW              = wm_prog_data->uses_src_w;