Add IRQ Sharing; add USB OHCI backbone.

kernel/Makefile:
	register usb_ohci.s

kernel/kernel.s:
	include usb_ohci.s

kernel/am79c971.s:
	irq sharing.

kernel/idt.s:
	add IRQ Sharing.

kernel/pci.s:
	comment out the Apple USB PCI driver declaration, done in usb_ohci.s.

kernel/print.s:
	add macro PRINTBITSd.

kernel/usb.s:
	fix typo in usb_ehci class declaration.

	Add definition for Intel EHCI driver (VirtualBox).

	update ISR registration and handling for IRQ sharing.

kernel/usb_ohci.s:
	beginnings of the driver.

DOC/Specs/USB_OHCI_....pdf
	add USB OHCI specification.