Membar in PSPromotionManager::copy_unmarked_to_survivor_space could be relaxed.

( Please also refer to the similar membar relaxed in G1ParScanThreadState::do_copy_to_survivor_space )

Test results:
Per the specjbb2015 test results, it has about 8% improvement in critical.

VM options:
-Xms50g -Xmx50g -XX:+UseParallelGC -XX:ParallelGCThreads=24 -XX:+UseLargePages -XX:LargePageSizeInBytes=2m -XX:+UseBiasedLocking -XX:+AlwaysPreTouch -XX:-UseAdaptiveSizePolicy

Test Env:
Architecture: aarch64
Byte Order: Little Endian
CPU(s): 128
On-line CPU(s) list: 0-127
Thread(s) per core: 1
Core(s) per socket: 64
Socket(s): 2
NUMA node(s): 4
Vendor ID: 0x48
Model: 0
Stepping: 0x1
BogoMIPS: 200.00
L1d cache: 64K
L1i cache: 64K
L2 cache: 512K
L3 cache: 65536K
NUMA node0 CPU(s): 0-31
NUMA node1 CPU(s): 32-63
NUMA node2 CPU(s): 64-95
NUMA node3 CPU(s): 96-127