[turbofan] simplify gap ordering

BUG=

Review URL: https://codereview.chromium.org/810013002

Cr-Commit-Position: refs/heads/master@{#25865}
[turbofan] remove control field from instruction

R=titzer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/810023002

Cr-Commit-Position: refs/heads/master@{#25866}