RFR: 8077615: AARCH64: Add C2 intrinsic for BigInteger::multiplyToLen() method

[Andrew Haley]

Follows x86, but changed to a more idiomatic AArch64 style for
efficiency.

I strengthened the regression test.  As fasr as I can see it doesn't
robustly check a corner case for carry propagation (i.e. when there is
a double carry.)  This is very easy to get wrong, so I added it.

http://cr.openjdk.java.net/~aph/8077615/

Andrew.