s390/sclp: reword cpu capability change message

Change wording for the cpu capabiity changed message:
If such an event occurs it only means that a cpu capability *may* have
changed. A cpu capability change event may also occur for other reasons.

Also change the severity of the message from warning to informational.

If such an event happens user space should into /proc/sysinfo and verify
if some capability values changed, if that is of interest.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>