enable io/memory unconditionally

enable io/memory unconditionally

VGA adapters need to claim memory and i/o
transactions even if they do not have any
i/o or memory bars. E.g. PCI spec, page 297,
gives an example of such a device:

    Programming interface 0000 0000b
    VGA-compatible controller. Memory
    addresses 0A 0000h through 0B
    FFFFh. I/O addresses 3B0h to 3BBh
    and 3C0h to 3DFh and all aliases of
    these addresses.

While we could check for these devices and special-case them, it is
easier to fix this by enabling i/o and memory space unconditionally:
devices that do not support it will just ignore this setting.

Original-by: Michael S. Tsirkin <mst@redhat.com>