phy: rockchip-inno-usb2: support otg vbus always powered on

phy: rockchip-inno-usb2: support otg vbus always powered on

Some platforms (e.g. RK3399 BOX board) otg port connector
interface is not standard, that is a Type-A connector with
vbus always powered on, looks like to work as host mode,
however, the otg port still need to support DRD mode.

In the current code, if otg vbus is always powered on, it
will cause USB2 PHY to detect a floating charger in error
case and power off USB2 PHY. This patch adds a new property
"rockchip,vbus-always-on" to fix this issue. With this patch,
we handle this case as otg host only mode, and avoid to do
charger detection and power off USB2 PHY.

Change-Id: I69e5e87021f3f2d654793e547264aec55ac664ef
Signed-off-by: William Wu <wulf@rock-chips.com>