S390 [simd]: cleanup the instruction selector

This CL includes the following changes:
- Avoid using `UniqueRegister` as much as possible
- Try to group opcodes under Binary or Unary when possible

Separate selectors are added to use `UniqueRegister` when necessary
mainly when `Temp` registers are used. This is to make sure temp, dst
and src registers are allocated differently and cannot be overwritten
during codegen.

Some codegen ops had to also be modified to avoid using `Temp`
registers.

Change-Id: I4d5bdec58cb4874e7c3d344091cde8c8a9a4d01b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3024149Reviewed-by: Junliang Yan <junyan@redhat.com>
Commit-Queue: Milad Fa <mfarazma@redhat.com>
Cr-Commit-Position: refs/heads/master@{#75723}