cpufreq: interactive: only apply interactive boost when enabled

Only apply the interactive boost when the interactive governor is
enabled.  This seems like the right thing to do.

This was originally reviewed on
	https://chromium-review.googlesource.com/273501



Change-Id: I5f4a7320683eada099f9a4253e3d6b0f03057fe8
Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Dmitry Torokhov <dtor@google.com>