qemu: make cirrus init value pci spec compliant

PCI memory should be disabled at reset, otherwise
we might claim transactions at address 0.
I/O should also be disabled, although for cirrus
it is harmless to enable it as we do not
have I/O bar.

Note: bios fix needed for this patch to work
was already applied:
previously bios incorrently assumed that it does not
need to enable i/o unless device has i/o bar.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>