RFR 8213203: [JVMCI] adopt formatting changes from jvmci 8

[Tom Rodriguez]

http://cr.openjdk.java.net/~never/8213203/webrev
https://bugs.openjdk.java.net/browse/JDK-8213203

This brings over primarily formatting changes from graal-jvmci-8 to 
partially synchronize the sources.  Mostly these are documentation 
improvements and style cleanups.  There are also some changes to reduce 
the visibility of non-public classes in the public API.  Testing is 
underway.

tom