aarch64: some regressions introduced by addition of vectorisation code

The recent addition of vectorisation code introduced a number of regressions

java/math/BigInteger/BigIntegerTest.java

fails with an assertion failure when run with fastdebug or slowdebug builds

# Internal Error (/home/alexander/build-open-jdk/dev/jdk9/baseline/dev/hotspot/src/cpu/aarch64/vm/assembler_aarch64.hpp:2078), pid=8124, tid=0x0000007ec61eb1f0
# assert(op == 0 && 0 == 0) failed: must be MOVI

and also in test

java/math/BigInteger/ModPow.java

java.math.BigInteger::add([I[I)[I gets miscompiled. There is a

        ldr q16, [x17,x10,lsl #4]

which should be a

        ldr q16, [x17,x10]