ASoC: wm_hubs: Special case headphones for digital paths in more use cases

The optimisations which we can do with caching the headphone DCS result in
wm_hubs have only been enabled in cases where class W is enabled. However,
there are more use cases which can benefit from the cache, especially with
WM8994 series devices with their more advanced digital routing.

Rather than keying off the class W information from the CODECs have a
check in wm_hubs for a suitable path and use that to determine if we can
deploy our headphone optimisations.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>