Kernel/USB: Add basic root port detection/management

We can now read/write to the two root ports exposed to the
UHCI controller, and detect when a device is plugged in or
out via a kernel process that constantly scans the port
for any changes. This is very basic, but is a bit of fun to see
the kernel detecting hardware on the fly :^)

Kernel/init.cpp

@@ -247,6 +247,7 @@ void init_stage2(void*)
     }
 
     USB::UHCIController::detect();
+    USB::UHCIController::the().spawn_port_proc();
 
     E1000NetworkAdapter::detect();
     RTL8139NetworkAdapter::detect();