Code is often being patched after creating, thus we don't need to flush
the icache right away.
This CL introduces a new enum to specify whether the icache should be
flushed or not, and uses this in all methods which don't always need to
flush.

Drive-by: Fix a but where SKIP_ICACHE_FLUSH was interpreted as boolean
value.

R=mstarzinger@chromium.org

Change-Id: I13ac71d2a7168a065b8a4a1086c590816de8ca28
Reviewed-on: https://chromium-review.googlesource.com/971881Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52102}