(11) RFR (S) JDK-8197956: VS2017 (C4838) Narrowing conversion required from __int64 to julong

[Lois Foltan]

Please review this fix to use the correct typed constant when 
initializing the StubRoutines::x86::_k512_W array.

open webrev at http://cr.openjdk.java.net/~lfoltan/bug_jdk8197956/webrev/
bug https://bugs.openjdk.java.net/browse/JDK-8197956
contributed-by: Kim Barrett & Lois Foltan

Testing complete (hs-tier1-3, jdk-tier1-3)