PM / devfreq: event: Find the instance of devfreq-event device by using phandle

This patch use the phandle to find the instance of devfreq-event device in
Device Tree when calling the devfreq_event_get_edev_by_phandle() because there
is two type devfreq-event devices as following:

First case, exynos-ppmu.c driver provides the maximum four event of each PPMU.
So, when getting the instance of devfreq-event device, using the unique name of
struct devfreq_event_desc.

Second case, exynos-nocp.c driver provide the only one event of each NoC Probe
device. So, when getting the instance of devfreq-event device, using the
phandle of each NoC probe device.

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Acked-by: MyungJoo Ham <myungjoo.ham@samsung.com>