softpipe: Increase the GLSL feature level

This will enable calls to the interpolateAt* functions, but also a bunch
of other features.

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>

src/gallium/drivers/softpipe/sp_screen.c

@@ -159,7 +159,7 @@ softpipe_get_param(struct pipe_screen *screen, enum pipe_cap param)
    case PIPE_CAP_MIXED_COLORBUFFER_FORMATS:
       return 1;
    case PIPE_CAP_GLSL_FEATURE_LEVEL:
-      return 330;
+      return 400;
    case PIPE_CAP_GLSL_FEATURE_LEVEL_COMPATIBILITY:
       return 140;
    case PIPE_CAP_QUADS_FOLLOW_PROVOKING_VERTEX_CONVENTION: