RFR: 8259822: [PPC64] Support the prefixed instruction format added in POWER10 [v4]

[Kazunori Ogata]

> The POWER10 processor, which implements Power ISA 3.1 [1], supports new instruction formats where an instruction takes two 32bit words.  The first word is called prefix, and the instructions with prefix are called prefixed instructions.  With more bits in opcode and operand fields, POWER10 supports larger immediate value in an operand, as well as many new instructions.
> 
> This is the first changes to handle prefixed instructions, and this adds support of prefixed addi (= paddi) instruction as an example of prefix usage.  paddi accepts 34bit immediate value, while original addi accepts 16bit value.
> 
> [1] https://ibm.ent.box.com/s/hhjfw0x0lrbtyzmiaffnbxh2fuo0fog0

Kazunori Ogata has updated the pull request incrementally with one additional commit since the last revision:

  Removed pla and psubi and adjusted spacing based on review comments

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2095/files
  - new: https://git.openjdk.java.net/jdk/pull/2095/files/a8770539..9d606d67

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2095&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2095&range=02-03

  Stats: 23 lines in 3 files changed: 2 ins; 6 del; 15 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2095.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2095/head:pull/2095

PR: https://git.openjdk.java.net/jdk/pull/2095