pci: add pci test device

This device is used for kvm unit tests,
currently it supports testing performance of ioeventfd.
Using updated kvm unittest, here's an example output:
mmio-no-eventfd

pci: add pci test device

This device is used for kvm unit tests,
currently it supports testing performance of ioeventfd.
Using updated kvm unittest, here's an example output:
mmio-no-eventfd:pci-mem 8796
mmio-wildcard-eventfd:pci-mem 3609
mmio-datamatch-eventfd:pci-mem 3685
portio-no-eventfd:pci-io 5287
portio-wildcard-eventfd:pci-io 1762
portio-datamatch-eventfd:pci-io 1777

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

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