RFR: 8351666: [PPC64] Make non-volatile VectorRegisters available for C2 register allocation

[Martin Doerr]

This PR makes the non-volatile VectorRegisters available for C2's register allocation.

I had to implement the VectorRegisters properly (4 VM Regs) like on other platforms. The old version has run into assertions and looked strange.

The non-volatile VectorRegisters are now saved when entering Java: call_stub and upcall_stubs.
I have rewritten the save and restore functions and used them for both. Then, I have removed code which has become dead. I only save and restore them if C2 uses the vector instructions (controlled by `SuperwordUseVSX`).
I have moved the non-volatile spill area out of the entry_frame_locals because it has a variable size, now.

The stack area for all non-volatile registers has become larger than the 288 Bytes which are allowed to be used below the SP (specified by the ABI). Therefore, I had to rewrite the call_stub sequence significantly. We need to push the new frame before saving the registers, now.

Saving and restoring the FP registers is not needed in the slow signature handler which also uses the save and restore code for non-volatile registers.

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Commit messages:
 - C2: Specify VSR52-63 as SOE and revert commit 2.
 - Fix register classification.
 - Update Copyright headers.
 - Add missing alignment in upcall stub frames.
 - Avoid redundant nv VR spill code in CRC stubs.
 - 8351666: [PPC64] Make non-volatile VectorRegisters available for C2 register allocation

Changes: https://git.openjdk.org/jdk/pull/23987/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23987&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8351666
  Stats: 829 lines in 13 files changed: 328 ins; 245 del; 256 mod
  Patch: https://git.openjdk.org/jdk/pull/23987.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23987/head:pull/23987

PR: https://git.openjdk.org/jdk/pull/23987