PM / devfreq: event: Change prototype of devfreq_event_get_edev_by_phandle function

Previously, devfreq core support 'devfreq-events' property in order to get
the devfreq-event device by phandle. But, 'devfreq-events' property name is
not proper on devicetree binding because this name doesn't mean
the any h/w attribute.

The devfreq-event core hand over the rights to decide the property name
for getting the devfreq-event device on devicetree. Each devfreq-event driver
will decide the property name on devicetree binding and then pass
the their own property name to devfreq_event_get_edev_by_phandle function.

And change the prototype of devfreq_event_get_edev_count function
because of used deprecated 'devfreq-events' property.

Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>