[turbofan] Mark MachineType as uint16_t.

[turbofan] Mark MachineType as uint16_t.

This fixes a few funky implicit conversions for the enum (that are
inconsistent across compilers) and also helps to save space, i.e. for
the representations_ vector in the InstructionSequence.

R=svenpanne@chromium.org

Committed: https://crrev.com/f588b1c55030db751f6e9dde08b572a859149754
Cr-Commit-Position: refs/heads/master@{#29011}

[Benedikt Meurer, 2015-06-15 05:31:14]

Hey Sven,

Some simple cleanup. Please take a look.

Thanks,
Benedikt

[Sven Panne, 2015-06-15 06:25:49]

The CQ bit was checked by svenpanne@chromium.org

[Sven Panne, 2015-06-15 06:25:49]

lgtm

[commit-bot: I haz the power, 2015-06-15 06:25:53]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1182303003/1

[commit-bot: I haz the power, 2015-06-15 06:27:14]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-15 06:27:33]

Patchset 1 (id:??) landed as
https://crrev.com/f588b1c55030db751f6e9dde08b572a859149754
Cr-Commit-Position: refs/heads/master@{#29011}