RFR: 8332265: RISC-V: Materialize pointers faster by using a temp register

[Robbin Ehn]

Hi, please consider!

Materializing a 48-bit pointer, using an additional register, we can do with:
lui + lui + slli + add + addi
This 15% faster both on VF2 and in CPU models, compared to movptr().

As we often materialize during calls there is free registers.

I have choose just a few spot to use it, many more can use.
E.g. la() with tmp register can use li48 instead of movptr.

Running tests now (so far so good), as if I screwed up IC calls it should be seen fast.
And benchmarks when hardware is free.

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Commit messages:
 - li48

Changes: https://git.openjdk.org/jdk/pull/19246/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19246&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8332265
  Stats: 168 lines in 6 files changed: 130 ins; 4 del; 34 mod
  Patch: https://git.openjdk.org/jdk/pull/19246.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19246/head:pull/19246

PR: https://git.openjdk.org/jdk/pull/19246