Maximum semispace size was capped at kMaxSemiSpaceSize. Also allow
non-power-of-2 sizes.

Change-Id: I3385674a13455b47802a3f6e62ac5b9ed3987264
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1962863Reviewed-by: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65445}