iris: bump compat profile support to 4.6

All of the current piglit compat profile tests pass.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/gallium/drivers/iris/iris_screen.c

@@ -230,9 +230,8 @@ iris_get_param(struct pipe_screen *pscreen, enum pipe_cap param)
    case PIPE_CAP_MAX_STREAM_OUTPUT_INTERLEAVED_COMPONENTS:
       return BRW_MAX_SOL_BINDINGS;
    case PIPE_CAP_GLSL_FEATURE_LEVEL:
-      return 460;
    case PIPE_CAP_GLSL_FEATURE_LEVEL_COMPATIBILITY:
-      return 140;
+      return 460;
    case PIPE_CAP_CONSTANT_BUFFER_OFFSET_ALIGNMENT:
       /* 3DSTATE_CONSTANT_XS requires the start of UBOs to be 32B aligned */
       return 32;