drivers/base: Extend documentation with preferred way to use auxbus

Document the preferred way to use auxiliary bus.

Signed-off-by: Leon Romanovsky <leon@kernel.org>
Link: https://lore.kernel.org/r/206e8c249f630abd3661deb36b84b26282241040.1743510317.git.leon@kernel.org


[ reworded the text a bit - gregkh ]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>