[aarch64-port-dev ] RFR(XS) 8233337: Shenandoah: Cleanup AArch64 SBSA::load_reference_barrier_not_null()

[Zhengyu Gu]

Please review this cleanup patch suggested by Andrew Haley. Please see 
[1] for details


Bug: https://bugs.openjdk.java.net/browse/JDK-8233337
Webrev: http://cr.openjdk.java.net/~zgu/JDK-8233337/webrev.00/

Test:
   hotspot_gc_shenandoah (fastdebug and release)
   on AArch64 Linux

Thanks,

-Zhengyu




[1] 
https://mail.openjdk.java.net/pipermail/shenandoah-dev/2019-October/010976.html