RFR (S): 8034868 Extract G1 From Card Cache into separate class

[Thomas Schatzl]

Hi all,

  can I get reviews for the following small change? It extracts the from
card cache previously embedded into the OtherRegionsTable into a
separate class, named FromCardCache.

This cleans up the remembered set somewhat.

While looking through the code I found that the remembered set code
still using int's for thread id's. I did not clean that up here, created
a new CR instead (https://bugs.openjdk.java.net/browse/JDK-8036116)
since that change would ripple through to quite a few places.

Webrev:
http://cr.openjdk.java.net/~tschatzl/8034868/webrev/

CR:
https://bugs.openjdk.java.net/browse/JDK-8034868

Testing:
JPRT

Thanks,
  Thomas