RFR: 8155245: Add logging when MMU target is violated

[Stefan Johansson]

Hi,

Please review this small change to add logging for MMU violations:
https://bugs.openjdk.java.net/browse/JDK-8155245

Webrev:
http://cr.openjdk.java.net/~sjohanss/8155245/hotspot.00/

Summary:
Add a log line when spending more time then allowed in GC, also added a 
new tag "mmu" and made sure it is associated with the GC-id.

Testing:
JPRT

Thanks,
Stefan