Add rktcphy(4), a driver for the Type-C PHY controller found on the

Add rktcphy(4), a driver for the Type-C PHY controller found on the
Rockchip RK3399.  While the PHY allows switching between combinations
of USB3 and DisplayPort, this driver enables only USB3 functionality.
This allows USB3 devices to show up on machines where previously only
USB2 devices showed up.  Driver was taken from FreeBSD and adjusted to
fit into our code base.

ok kettenis@