usb: dwc3: support runtime power management for rockchip platform

usb: dwc3: support runtime power management for rockchip platform

This patch adds runtime power management support for rockchip platform.
It depends on extcon notifier to do runtime resume and runtime suspend.
And since the dwc3 core dev is the only child of dwc3 rockchip dev, so
we need to ensure dwc3 core dev enter runtime suspend befer put dwc3
rockchip dev in runtime suspend. And after do runtime resume dwc3 core
dev, the PM core will resume dwc3 rockchip dev prior to dwc3 core dev
resume. With this patch, we can power off USB3 power domain and disable
clocks in runtime suspend.

Change-Id: Ib529889a8603d12dcdce80e9e0716be44c028bd3
Signed-off-by: Wu Liang feng <wulf@rock-chips.com>