Broaden test expectation for ARM64.

R=machenbach@chromium.org
BUG=v8:3154
TEST=cctest/test-heap/ReleaseOverReservedPages

Review URL: https://codereview.chromium.org/270303005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21192 ce2b1a6d-e550-0410-aec6-3dcde31c8c00