i386: clarify that the Q35 machine type implements a P35 chipset

i386: clarify that the Q35 machine type implements a P35 chipset

The 'q35' machine type implements an Intel Series 3 chipset,
of which there are several variants:

  https://www.intel.com/Assets/PDF/datasheet/316966.pdf

The key difference between the 82P35 MCH ('p35', PCI device ID 0x29c0)
and 82Q35 GMCH ('q35', PCI device ID 0x29b0) variants is that the latter
has an integrated graphics adapter. QEMU does not implement integrated
graphics, so uses the PCI ID for the 82P35 chipset, despite calling the
machine type 'q35'. Thus we rename the PCI device ID constant to reflect
reality, to avoid confusing future developers. The new name more closely
matches what pci.ids reports it to be:

$ grep  P35 /usr/share/hwdata/pci.ids  | grep 29
	29c0  82G33/G31/P35/P31 Express DRAM Controller
	29c1  82G33/G31/P35/P31 Express PCI Express Root Port
	29c4  82G33/G31/P35/P31 Express MEI Controller
	29c5  82G33/G31/P35/P31 Express MEI Controller
	29c6  82G33/G31/P35/P31 Express PT IDER Controller
	29c7  82G33/G31/P35/P31 Express Serial KT Controller

$ grep  Q35 /usr/share/hwdata/pci.ids  | grep 29
	29b0  82Q35 Express DRAM Controller
	29b1  82Q35 Express PCI Express Root Port
	29b2  82Q35 Express Integrated Graphics Controller
	29b3  82Q35 Express Integrated Graphics Controller
	29b4  82Q35 Express MEI Controller
	29b5  82Q35 Express MEI Controller
	29b6  82Q35 Express PT IDER Controller
	29b7  82Q35 Express Serial KT Controller

Arguably the QEMU machine type should be named 'p35'. At this point in
time, however, it is not worth the churn for management applications &
documentation to worry about renaming it.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20180830105757.10577-1-berrange@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>