soundwire: Add a helper function to wait for device initialisation

soundwire: Add a helper function to wait for device initialisation

Add a new helper function to wait for the device to enumerate
and be initialised by the SoundWire core. Most of the SoundWire
drivers have very similar boiler plate code in their runtime
resume, and that boiler plate tends to access various internals
of the SoundWire structs which is a mild layering violation.

Adding a new core helper function greatly eases both of these
issues.

Acked-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://patch.msgid.link/20260512103022.1154645-2-ckeepax@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>