kobject: define common logging prefix

All log messages start with the prefix "kobject: ".
Deduplicate this by using the pr_fmt() facility.

This makes the very long log strings shorter.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/r/20230311-kobject-warning-v1-1-1ebba4f71fb5@weissschuh.net


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>