Changes

Use OMRPORT_CPU_TARGET for split list calculation

For Flat heap GCs, use OMRPORT_CPU_TARGET (rather than
OMRPORT_CPU_ONLINE). It really is the number of h/w threads available to
JVM process, if configured in a container or by some other OS specific
means.

Same TARGET is used for other (and indirectly related) GC thread count
caculation.

Signed-off-by: Aleksandar Micic <Aleksandar_Micic@ca.ibm.com>
 (commit: 40aab8f)