This adds a simple EHCI driver that currently only interrogates the
device and checks if all ports are addressable via associated legacy
controllers (companion controllers), and warns if this is not the case.
This also adds a lot of the other data structures needed for actually
driving the controller, but these are currently not hooked up to
anything.
To test this run with `SERENITY_EXTRA_QEMU_ARGS="--device usb-ehci"`
or the q35 machine type
