Document more bus addresses.

Update for bugs fixed.

Describe where exactly the -drive options go.

Update for recent split of qdev ide-drive into ide-{cd,hd},
scsi-disk into scsi-{cd,hd}.

Document scsi-hd's removable property only for usb-storage, because
that's where it's used.

Fix description of -global isa.fdc.

Document usb-storage lossage.

Clean up misleading description of network device's split into guest
and host part.

Document -vga's machine dependence.

New qdevs: virtconsole, qxl-vga, isa-vga, intel-hda, usb-ccid

Update for changed pci-assign property iommu.

New section "Default Devices".

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>