Most MIPS64 processors have user space of 2^40 bytes. Therefore,
we need to lower the address space limit in WasmMemoryTracker
for this particular architecture.

Change-Id: Ic9945af7a15ecba7dfabfe996140941ada089b2a
Reviewed-on: https://chromium-review.googlesource.com/1079551Reviewed-by: Eric Holk <eholk@chromium.org>
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Cr-Commit-Position: refs/heads/master@{#53468}