softpipe: Report some sane values for constant buffer CAP queries.

src/gallium/drivers/softpipe/sp_screen.c

@@ -91,6 +91,10 @@ softpipe_get_param(struct pipe_screen *screen, int param)
       return 1;
    case PIPE_CAP_BLEND_EQUATION_SEPARATE:
       return 1;
+   case PIPE_CAP_MAX_CONST_BUFFERS:
+      return PIPE_MAX_CONSTANT_BUFFERS;
+   case PIPE_CAP_MAX_CONST_BUFFER_SIZE:
+      return 4096 * 4 * sizeof(float);
    default:
       return 0;
    }