Some ValueKinds were defined based on the size of a system pointer or
the size of a tagged value. In order to be able to reuse those
definitions in both LiftoffAssembler and LiftoffCompiler, define them as
public constants on LiftoffAssembler.
Also, avoid the "ValueType" suffix, since they are not ValueTypes, but
ValueKinds.

R=jkummerow@chromium.org

Change-Id: I38f9c9b6c4e6592d31ee58466b786bf24a55f19c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2743890Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73315}