RFR: 8263354: Accumulated C2 code cleanups

[Pengfei Li]

This is a trivial patch to cleanup C2 code at several places, including

- Remove duplicated node enumerations of MinV & MaxV in adlc functions
- Use "1<<X" to define LoopNode flags, like other C2 flag definitions
- Unify macro names in aarch64_sve_ad.m4: UNPREDICATE -> UNPREDICATED
- Delete redundant empty lines in aarch64_sve.ad

Tier1 tests passed.

-------------

Commit messages:
 - 8263354: Accumulated C2 code cleanups

Changes: https://git.openjdk.java.net/jdk/pull/2934/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2934&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8263354
  Stats: 64 lines in 4 files changed: 2 ins; 20 del; 42 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2934.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2934/head:pull/2934

PR: https://git.openjdk.java.net/jdk/pull/2934