RFR: JDK -8001933 Move Gensrc*.gmk and Gendata*.gmk into separate directories

[Magnus Ihse Bursie]

Bug: https://bugs.openjdk.java.net/browse/JDK-8001933

In the makefiles directory in the jdk repo, there are a lot of files -- 
important files, and lot of small helper files. Many of them share a 
common filename prefix; however, there is a better kind of namespaces to 
show hierarchy in file systems: directories! :-)

This fix moves all the "Gensrc*" files into the "gensrc" directory, and 
all the "Gendata*" into the "gendata" directory. The result is a clearer 
picture of the overall structure of the JDK build system.

WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8001933-move-gensrc-and-gendata/webrev.01

/Magnus