ASoC: wm_adsp: Add support for "toggle" preloaders

ASoC: wm_adsp: Add support for "toggle" preloaders

In the case a device can support retaining the firmware memory across
low power states it is useful for the preloader widget to only power up
whilst actually loading/unloading the core, as opposed to the normal
operation where the widget is powered for the entire time a firmware is
preloaded onto the core. Add support for this mode and a flag to enable
it.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20220105113026.18955-7-ckeepax@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>