RFR: 8227676: Shenandoah: More consistent naming of LRB entry points

[Roman Kennke]

Current naming of LRB runtime entry points is a bit weird. We have:

- load_reference_barrier_JRT (where _JRT doesn't serve any purpose)
- oop_load_from_native_barrier (which is really like LRB except loading
from native memory)

I propose to rename to:
- load_reference_barrier
- load_reference_barrier_native

    Options


Bug:
https://bugs.openjdk.java.net/browse/JDK-8227676
Webrev:
http://cr.openjdk.java.net/~rkennke/JDK-8227676/webrev.00/

Testing: hotspot_gc_shenandoah

Ok?
Roman