[8u40] RFR(L) 8055494: Add C2 x86 intrinsic for BigInteger::multiplyToLen() method

[Vladimir Kozlov]

Backport request. The fix was pushed into jdk9 last week.
Changes were applied cleanly.

https://bugs.openjdk.java.net/browse/JDK-8055494
jdk9 webrev:
http://cr.openjdk.java.net/~kvn/8055494/webrev/
jdk9 changeset:
http://hg.openjdk.java.net/jdk9/hs-comp/hotspot/rev/427de14928ab

Thanks,
Vladimir