atkbdc - Do not attach PS2 controller via legacy ISA bus, if FADT says so.

atkbdc - Do not attach PS2 controller via legacy ISA bus, if FADT says so.

* If the FADT BootFlags value tells us that we shouldn't expect the PS2
  controller to be at the IO ports 0x60/0x64, we should instead only attach
  the atkbdc driver when there is a matching device in the ACPI namespace.

* This avoids attempts to attach the atkbdc PS2 controller driver on
  hardware which doesn't have a usable PS2 controller. This happens on
  many modern notebooks, and has been the case for some time on desktop
  hardware that doesn't provide an emulated PS2 controller for using USB
  input devices all the time (it either is never initialized, or might
  get disabled by some of the ACPI or USB initialization during bootup).