RFR: 8366076: arm32: Fix register allocation for vector instructions [v2]

[Max Verevkin]

> Arm32 has 32 double-precision floating point registers, the first 16 of which coincide with the 32 single-precision floating point registers. Some vector-operation nodes were implemented in terms of scalar instructions, which only really works for the first 16 doubles. This commit addresses that.

Max Verevkin has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  8366076: arm32: Fix register allocation for vector instructions
  
  Arm32 has 32 double-precision floating point registers, the first 16 of
  which coincide with the 32 single-precision floating point registers.
  Some vector-operation nodes were implemented in terms of scalar
  instructions, which only really works for the first 16 doubles. This
  commit addresses that.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/27071/files
  - new: https://git.openjdk.org/jdk/pull/27071/files/7b7f61fe..2faabeed

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27071&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27071&range=00-01

  Stats: 6 lines in 2 files changed: 0 ins; 5 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/27071.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27071/head:pull/27071

PR: https://git.openjdk.org/jdk/pull/27071