MIPS64 requires that each allocated page is aligned to 256 MB.
This is so because we use J instruction for long branches
that are withing a 256 MB block of code.

Change-Id: I1222842a5b8ecfacc0397a744ab464e9a747f8b7
Reviewed-on: https://chromium-review.googlesource.com/901611
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51110}