[vector] Refactor vector operations in aarch64 backend

[Yang Zhang]

Hi,

Please help to review this patch that refactor vector operations in aarch64 backend.

Summary: move all vector operations which are not in jdk master to
aarch64_neon_ad.m4 and place generated instructions to the end of aarch64.ad.
This change is to minimize conflict when merging Vector API to jdk
master. In reduction operations, identify scalar/vector input as isrc/
vsrc to make code clear. Jdk master also uses such naming style.

http://cr.openjdk.java.net/~yzhang/vectorapi/vectorapi.refactor/webrev.00/

Regards
Yang