RFR(L) 8001532: C2 node files refactoring

[Morris Meyer]

Folks,

Could I get a review for 8001532 - refactoring the old connode file in 
the C2 source tree?

I've broken connode into bitsnode, castnode, constnode, convertnode, 
movenode, narrownode, optonode and threadnode.

This change has been through JPRT.

         --morris meyer

JBS - https://bugs.openjdk.java.net/browse/JDK-8001532
WEBREV - http://cr.openjdk.java.net/~morris/8001532.01