Remove unused and commented out sc_dma_reserve
Fix (harmless?) bug that set the roothub address to the device address.
Rework roothub control transfers so that much of the code is shared
across HCDs.

I have retained the vendor/product reporting for each HCD for now,
but it maybe get removed later.

ahci(4) now reports a language table and uses the usb_makestrdesc
function instead of rolling its own version.