[turbofan] cleanup InstructionOperand a little

[turbofan] cleanup InstructionOperand a little

- ConstantOperand was using a too-small field too store its virtual register
- drop ConvertTo, replace it with simple copy
- split AllocatedOperand off from Immediate and Constant to make assignment clearer, also paving the way for small Immediates
- put zone first in *Operand::New
- driveby: drop delayed ssa deconstruction experiment

R=titzer@chromium.org
BUG=

Committed: https://crrev.com/07ff6d9f22de49e5d9d8b2215864228e136a6cf5
Cr-Commit-Position: refs/heads/master@{#27692}

[dcarney, 2015-04-02 09:12:38]

dcarney@chromium.org changed reviewers:
+ titzer@chromium.org

[dcarney, 2015-04-02 09:13:00]

ptal

[dcarney, 2015-04-02 09:32:14]

Patchset #6 (id:100001) has been deleted

[Benedikt Meurer, 2015-04-09 09:09:28]

bmeurer@chromium.org changed reviewers:
+ bmeurer@chromium.org

[Benedikt Meurer, 2015-04-09 09:09:28]

lgtm

[dcarney, 2015-04-09 09:14:00]

The CQ bit was checked by dcarney@chromium.org

[commit-bot: I haz the power, 2015-04-09 09:14:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1050803002/140001

[commit-bot: I haz the power, 2015-04-09 09:15:33]

Committed patchset #7 (id:140001)

[commit-bot: I haz the power, 2015-04-09 09:15:44]

Patchset 7 (id:??) landed as
https://crrev.com/07ff6d9f22de49e5d9d8b2215864228e136a6cf5
Cr-Commit-Position: refs/heads/master@{#27692}