PPC/s390: [codegen] Change RegList into a class

Port 8a0d1b6f

Original Commit Message:

    Modernise the RegList interface to be a proper class, rather than a
    typedef to an integer, and add proper methods onto it rather than ad-hoc
    bit manipulation.

    In particular, this makes RegList typesafe, adding a DoubleRegList for
    DoubleRegisters.

    The Arm64 CPURegList isn't updated to use (or extend) the new RegList
    interface, because of its weird type-erasing semantics (it can store
    Registers and VRegisters). Maybe in the future we'll want to get rid of
    CPURegList entirely and use RegList/DoubleRegList directly.

R=leszeks@chromium.org, joransiu@ca.ibm.com, junyan@redhat.com, midawson@redhat.com
BUG=
LOG=N

Change-Id: I997156fe4f4f2ccc40b2631d5cb752efdc8a5ad2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3525084


Reviewed-by: Junliang Yan <junyan@redhat.com>
Commit-Queue: Milad Farazmand <mfarazma@redhat.com>
Cr-Commit-Position: refs/heads/main@{#79484}