G1: Move static initialization of G1FromCardCache to a proper location

in src/hotspot/share/gc/g1/g1RemSet.cpp:

 488 void G1RemSet::initialize(uint max_reserved_regions) {
 489 G1FromCardCache::initialize(num_par_rem_sets(), max_reserved_regions);
 490 _scan_state->initialize(max_reserved_regions);
 491 }

the static initialization is piggy-backed to G1RemSet instance initialization which is rather bad code. Fortunately there is only one G1RemSet instance and that method is only called once so no functional issue.

Move that initialization.