PM / devfreq: rk3399_dmc: remove wait for dcf irq event.

We have already wait dcf done in ATF, so don't need wait dcf irq
in kernel, besides, clear dcf irq in kernel will import competiton
between kernel and ATF, only handle dcf irq in ATF is a better way.

Signed-off-by: Lin Huang <hl@rock-chips.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>