MIPS64 has a user space of 2^40 bytes on most processors, address
space limits needs to be smaller. 256G is ok, but it will cause
mjsunit/wasm/bulk-memory-spec/memory_copy.wast get a OOM error.

Bug: v8:7747
Change-Id: Ie7a96336ef4ab6340def813478a09bdf3f76894e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1605524
Auto-Submit: Yu Yin <xwafish@gmail.com>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61417}