RFR: JDK-8047874 - Migrate GPIO Changes From Internal Repos

[Jen Dority]

issue: https://bugs.openjdk.java.net/browse/JDK-8047874
webrev: http://cr.openjdk.java.net/~jld/8047874/

Hi All,

Please review my changes for JDK_8047874. These changes refactor the 
GPIO implementation, undoing a lot of the raspberry pi-specific 
configuration checking.

Thanks,
Jen