Samus: Handle fan startup in the EC, not the fan controller

The fans on samus have a recommended minimum duty cycle of 20%
while running, but 30% in order to start. We've been using the
EC's built-in fan controller for the start requirement, but it
has a minimum fast-start duty cycle of 50%. It turns out that
that speed is noticeably noisy.

This change handles the startup with logic in the EC instead, so
that the fan only tries to spin at 30% initially (or if it drops
too much below the minimum turning speed).

BUG=chrome-os-partner:33429
BRANCH=ToT,samus
TEST=make buildall -j

Boot the system, let it idle with the browser windows closed, the
browse a bit, then idle. Listen for changes to the fans.

Before, I could hear the fans kick in and out as the AP load
changed. Now it's much quieter.

Change-Id: Id35215520c064eb6843686ec8bb5f3618dac6cf6
Signed-off-by: Bill Richardson <wfrichar@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/227658
Reviewed-by: Randall Spangler <rspangler@chromium.org>

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