RFR (M): 8153507: Improve Card Table Clear Task

[Thomas Schatzl]

Hi all,

  during performance measurements of the Card Table Clear task it has
been shown that the current way of distributing work is way too fine
grained. Threads are stalling most of the time on the atomic cmpxchg
during work distribution instead of doing work.

This change tries to fix this by changing the way how the "dirty"
regions are stored from a single linked list to a set of region
indices, where the usual claim-by-chunks technique can be applied.

Further using we can effectively limit the number of threads used by
the API introduced by JDK-8155232.

Third, by reorganizing the code into the g1RemSet files, clutter across
the g1 code is minimized.

CR:
https://bugs.openjdk.java.net/browse/JDK-8153507
Webrev:
http://cr.openjdk.java.net/~tschatzl/8153507/webrev/
Testing:
jprt, vm.gc testlist

Thanks,
  Thomas