RFR: 8264412: AArch64: CPU description should refer DMI

[Yasumasa Suenaga]

`jdk.CPUInformation` event on AArch64 has valid CPU description in [JDK-8262491](https://bugs.openjdk.java.net/browse/JDK-8262491), however it does not work on UEFI booted machine.

[JDK-8262491](https://bugs.openjdk.java.net/browse/JDK-8262491) refers device tree to get board name, however it does not exist on UEFI. We need to refer DMI.
However we need to have root privilege, so we refer /sys/devices/virtual/dmi/id to avoid it.

We can get board name from /sys/devices/virtual/dmi/id/board_name, but some machine set empty string to it. So we will refer /sys/devices/virtual/dmi/id/product_name as a fallback.

For example, we can get following CPU description on AWS A1 instance after this change:

jdk.CPUInformation {
  startTime = 05:28:24.506
  cpu = "AArch64"
  description = "AArch64 a1.2xlarge  0x41:0x0:0xd08:3, simd, crc, aes, sha1, sha256"
  sockets = 8
  cores = 8
  hwThreads = 8
}

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

Commit messages:
 - refactoring
 - 8264412: AArch64: CPU description should refer DMI

Changes: https://git.openjdk.java.net/jdk/pull/3259/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3259&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264412
  Stats: 22 lines in 1 file changed: 13 ins; 3 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3259.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3259/head:pull/3259

PR: https://git.openjdk.java.net/jdk/pull/3259