LU-17995 libcfs: implement libcfs_subsystem_debug

LU-17995 libcfs: implement libcfs_subsystem_debug

Allow printk to be enabled based on subsystem. This mirrors
the existing infrastructure for printing debug messages
to console.

Also, include file and function names in debug messages
printed to the console.

These changes remove the need for the custom debugging in
the in-memory OSD.

Test-Parameters: trivial
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: Ifaca7f6d4f1b7b5fb42e7147b5a9dff0b34f643a
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/57336
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>