MLK-11333 ARM: imx: enable busfreq daemon by default

By default, busfreq mode is set to high bus mode,
if there is no high speed device enabled, system
should be able to enter low bus mode, that is why
we have a daemon thread created to handle such
scenario, this daemon should be enabled after busfreq
driver probed.

However, we missed to enable it before, this patch
enables it.

Signed-off-by: Anson Huang <b20788@freescale.com>