ASoC: wm_hubs: Factor out class W management

Since the analogue portions of the checks for class W are the same over
all the devices factor out these checks into wm_hubs and while we're at
it also use wm_hubs_dac_hp_direct() to enable class W optimisations on
more paths.

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