The {NONE} reloc info is the one used most often, i.e. for every
assembler call that takes an {Immediate} on x64 which is not
relocatable.
Hence assign value 0 to {NONE} such that constructing such immediates is
faster and also checking for this most common case is faster.

R=ishell@chromium.org

Bug: v8:10576
Change-Id: I3c048710b80dd31fa5b5d3b1415d72a24d95cb90
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2237136Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68259}