coding-style: Add guidance to prefer dev_dbg

During review, it was suggested that drivers only emit messages when
something is wrong or it is a debug message. Document this as a formal
recommendation.

https://lore.kernel.org/linux-usb/2024012525-alienate-frown-916b@gregkh/Signed-off-by: Abhishek Pandit-Subedi <abhishekpandit@chromium.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240125165311.1.I8d9c88e747e233917e527c7dad1feb8a18f070e2@changeid

Documentation/process/coding-style.rst

@@ -899,7 +899,8 @@ which you should use to make sure messages are matched to the right device
 and driver, and are tagged with the right level:  dev_err(), dev_warn(),
 dev_info(), and so forth.  For messages that aren't associated with a
 particular device, <linux/printk.h> defines pr_notice(), pr_info(),
-pr_warn(), pr_err(), etc.
+pr_warn(), pr_err(), etc. When drivers are working properly they are quiet,
+so prefer to use dev_dbg/pr_debug unless something is wrong.
 
 Coming up with good debugging messages can be quite a challenge; and once
 you have them, they can be a huge help for remote troubleshooting.  However