MSI is broken on SiS 761 chipset at least on PC Chips A31G board.  No
interrupts are delivered once MSI is enabled for a device.  This causes
hang on X11 start with a nVidia card installed (with nouveau driver).

Disable MSI completely for this chipset.
Signed-off-by: NOndrej Zary <linux@rainbow-software.org>
Signed-off-by: NBjorn Helgaas <helgaas@kernel.org>