ASoC: wm_adsp: Factor out common init code

Factor out the duplicated initialization statements from
wm_adsp1_init() and wm_adsp2_init() into new function
wm_adsp_common_init().

The entire content of wm_adsp1_init() is the common code
but it is convenient to retain this exported function
to hide what we currently treat as common init (which might
change in the future) and also make clear the difference
between an ADSP1 entry point and common code.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>