ASoC: wm_adsp: Warn that firmware file format 0 is depreciated

There are very few version 0 firmwares in the wild and at some point in
the future it would be nice to remove support for them from the driver,
as they require several work arounds to be present to create controls
properly.

This patch adds a depreciated warning if someone is using this file
format.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>