ASoC: arizona: Factor out speaker widgets from CODEC drivers

Some system designs have been identified which repurpose portions of the
speaker driver circuits for other functions which will require that they
not be managed using DAPM. Prepare for this by factoring out the creation
of the speaker widgets into the core driver, the widgets will be replaced
by dummy ones when the additional functions are enabled.

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