soundwire: Move wait for initialisation helper to header

soundwire: Move wait for initialisation helper to header

As SoundWire devices tend to enumerate on the bus after probe, drivers
frequently need to wait for the device to initialise from common driver
code. The common system is to split drivers into a core module and then
a module for each communication bus. These two facts tend to cause
Kconfig issues, the issue tends to be when SOUNDWIRE=m and DRIVER_I2C=y,
this usually selects DRIVER=y. The driver code then wants to call
sdw_slave_wait_for_init(), but this results in calling a module function
from built in code. A depends on SOUNDWIRE | !SOUNDWIRE could be added to
the end driver but this seems slightly off as it adds a lot of counter
intuitive depends.

A simpler solution is to make sdw_slave_wait_for_init() a static inline
function. As part of doing this add a check for the slave device being
NULL acknowledging that this is likely called from code that is shared
between control buses. It does require dropping the call to
sdw_show_ping_status() but this can be added back in end drivers that
used it originally.

Currently this is causing rand config issues on RT5682 and will soon
also cause similar problems on cs42l43.

Acked-by: Vinod Koul <vkoul@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://patch.msgid.link/20260623101814.24044-2-ckeepax@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>