Split the current FDT-only implementation up into an FDT and an
ACPI part. Split the softcs up into a "common" part and per-bus
version and use the common one for common functions needed by both.
Given we are dealing with 2.5 softcs don't used "sc" for xhci (now xsc)
or the common part (now csc). Switch to device_{get,has}_property
for common configuration and quirks handling.
This makes the Synopsis XHCI root hubs attach correctly on
SolidRun's HoenyComb instead of just the generic XHCI root and
this means we are also doing proper chip setup and applying the
quirk needed there [1].