Revert of [x64] Use xorl to materialize smi zero.

Revert of [x64] Use xorl to materialize smi zero. (patchset #1 id:1 of https://codereview.chromium.org/1085153002/)

Reason for revert:
Seems to cause performance regressions.

Original issue's description:
> [x64] Use xorl to materialize smi zero.
>
> Before we always loaded smi zero via a movabs with a 64-bit immediate,
> which is pretty expensive compared to the xorl.
>
> R=jarin@chromium.org
>
> Committed: https://crrev.com/f236777bfe6e080ff1ead6baf847cc9b6bb4f9cb
> Cr-Commit-Position: refs/heads/master@{#27829}

TBR=jarin@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:477592
LOG=n

Committed: https://crrev.com/c66a2f7b468cae9ef1972f0001bf4b8efef60f98
Cr-Commit-Position: refs/heads/master@{#27867}

[Benedikt Meurer, 2015-04-16 08:29:51]

Created Revert of [x64] Use xorl to materialize smi zero.

[Benedikt Meurer, 2015-04-16 08:29:59]

The CQ bit was unchecked by bmeurer@chromium.org

[Benedikt Meurer, 2015-04-16 08:30:22]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-04-16 08:30:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1059543004/1

[commit-bot: I haz the power, 2015-04-16 08:31:31]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-16 08:31:39]

Patchset 1 (id:??) landed as
https://crrev.com/c66a2f7b468cae9ef1972f0001bf4b8efef60f98
Cr-Commit-Position: refs/heads/master@{#27867}