phy: rockchip-inno-usb2: support tuning phy for rk3399

phy: rockchip-inno-usb2: support tuning phy for rk3399

This patch adds a method to tuning phy with the following
parameters to improve usb driver strength and increase usb2
compatibility.

1. Set max ODT compensation voltage and current tuning reference.
2. Set max pre-emphasis level.
3. Disable the pre-emphasize in eop state and chirp state
   to avoid mis-trigger the disconnect detection and also
   avoid hs handshake fail.

We don't enable the phy tuning by default. If you want to
tuning phy, you can add a property "rockchip,u2phy-tuning"
in u2phy node, like this:

&u2phy0 {
	rockchip,u2phy-tuning;
};

&u2phy1 {
	rockchip,u2phy-tuning;
};

Change-Id: Iaa70e2ad3d5d06662be6c05e4d20784e5bb85ae9
Signed-off-by: William Wu <wulf@rock-chips.com>