gallium/radeon: disable evergreen_do_fast_color_clear for BE

This function is currently broken for BE. I assume it's because of
util_pack_color(). Until I fix this path, I prefer to disable it so users
would be able to see correct colors on their desktop and applications.

Together with the two following patches:
- gallium/r600: Don't let h/w do endian swap for colorformat
- gallium/radeon: remove separate BE path in r600_translate_colorswap

it fixes BZ#72877 and BZ#92039

Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>
Cc: "11.1 11.2" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
(cherry picked from commit a640ad15e1)

src/gallium/drivers/radeon/r600_texture.c

@@ -1408,6 +1408,11 @@ void evergreen_do_fast_color_clear(struct r600_common_context *rctx,
 {
 	int i;
 
+	/* This function is broken in BE, so just disable this path for now */
+#ifdef PIPE_ARCH_BIG_ENDIAN
+	return;
+#endif
+
 	if (rctx->render_cond)
 		return;