RFR (XXS): 8145671: Rename FromCardCache to G1FromCardCache

[Thomas Schatzl]

Hi all,

  as the title for this change implies, this code changes the name of
the FromCardCache class into G1FromCardCache to adhere to other class
names.

It is based on 8145667.

CR:
https://bugs.openjdk.java.net/browse/JDK-8145671
Webrev:
http://cr.openjdk.java.net/~tschatzl/8145671/webrev/
Testing:
jprt

Thanks,
  Thomas