8148099: Improve memory access to FromCardCache during GC
Summary: Transpose the FromCardCache data array so the access during GC is linear instead of element-by-element with stride.
Reviewed-by: mgerdin, brutisso

8145672: Remove dependency of G1FromCardCache to HeapRegionRemSet
Summary: Move HeapRegionRemSet::num_par_rem_sets() to G1RemSet, and document it.
Reviewed-by: mgerdin, jmasa

8145671: Rename FromCardCache to G1FromCardCache
Reviewed-by: jmasa, mgerdin

8145667: Move FromCardCache into separate files
Reviewed-by: mgerdin, stefank