RFR (S): 8179679: Rearrange filters before card scanning

[Thomas Schatzl]

Hi all,

  please have a look at this change that rearranges the checks in the
G1RemSet card scanning a bit in order to:

- remove some redundant checking made possible recently with JDK-
8177044
- group together similar checks (so that the compiler can more easily
reuse some intermediate values)
- minimize unnecessary card claiming

CR:
https://bugs.openjdk.java.net/browse/JDK-8179679
Webrev:
http://cr.openjdk.java.net/~tschatzl/8179679/webrev.1/ (note: there has
been a previous webrev, but without reviews; still there is a
webrev.0_to_1 for the curious)
Testing:
jprt, performance regression analysis

Thanks,
  Thomas