driver: core: Improve documentation for fwnode_operations.add_links()

 *		links to all the suppliers of the device that are available at

 *		the time this function is called.  The function must NOT stop

 *		at the first failed device link if other unlinked supplier

 *		devices are present in the system.  If some suppliers are not

 *		yet available, this function will be called again when other

 *		devices are present in the system.  This is necessary for the

 *		driver/bus sync_state() callbacks to work correctly.

 *

 *		For example, say Device-C depends on suppliers Device-S1 and

 *		Device-S2 and the dependency is listed in that order in the

 *		firmware.  Say, S1 gets populated from the firmware after

 *		late_initcall_sync().  Say S2 is populated and probed way

 *		before that in device_initcall(). When C is populated, if this

 *		add_links() function doesn't continue past a "failed linking to

 *		S1" and continue linking C to S2, then S2 will get a

 *		sync_state() callback before C is probed. This is because from

 *		the perspective of S2, C was never a consumer when its

 *		sync_state() evaluation is done. To avoid this, the add_links()

 *		function has to go through all available suppliers of the

 *		device (that corresponds to this fwnode) and link to them

 *		before returning.

 *

 *		If some suppliers are not yet available (indicated by an error

 *		return value), this function will be called again when other

 *		devices are added to allow creating device links to any newly

 *		available suppliers.

 *