This is to address the first issue reported on v8:8453

Page::kPageSize is 524288
MemoryAllocator::GetCommitPageSize() returns 65536 on ppc

ObjectEndOffsetInCodePage() returns 458752
ObjectStartOffsetInCodePage() returns (65536 + 65536) => 131072

Therefore, memory = 327680, which is less than
kMaxRegularHeapObjectSize(507136), which causes the DCHECK to fail.

Bug: v8:8453
Change-Id: I6048192ded4234a6987371ec4d4b2a8553756c25
Reviewed-on: https://chromium-review.googlesource.com/c/1355422
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58001}