hg: panama/dev: Add support for VectorCast nodes

[yang.zhang at arm.com]

Changeset: 0785295027bc
Author:    yzhang
Date:      2020-02-14 11:50 +0800
URL:       https://hg.openjdk.java.net/panama/dev/rev/0785295027bc

Add support for VectorCast nodes
1. Add backend support for nodes VectorCast{B,S,I,L,F,D}2X on AArch64;
2. Add functions to encode assembly instructions
   fcvtl/fcvtn/scvtfs/scvtfd/scvtfv/sshll/sshll2/sxtl, which are
   needed when adding support for these nodes.

Contributed-by: qi.feng at arm.com

! src/hotspot/cpu/aarch64/aarch64.ad
! src/hotspot/cpu/aarch64/assembler_aarch64.hpp