lib/plist.c: make plist test announcements KERN_DEBUG

They show up in dmesg

[    4.041094] start plist test
[    4.045804] end plist test

without a lot of meaning so hide them behind debug loglevel.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>