vfio: Remove PCI dependency
vfio: Remove PCI dependency

VFIO-PCI device has its own region naming but eventually it starts from 0
(as well as it suppose for others VFIO device types) so simply use 0
instead of VFIO_PCI_BAR0_REGION_INDEX.
At the same time move PCI-specific checks to helper function for clarity.

BUG=b:185504618
TEST=manatee PCI device passthrough boots/works

Change-Id: I404a9585016d230c48a6db7248172d2381a0a3e1
Signed-off-by: Tomasz Nowicki <b295c12c5cac773cdf3a1a19682b55ac85268b42@semihalf.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2961213
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Commit-Queue: Tomasz Nowicki <a1603cf6334574df9b8204692b318701aeaf1ca1@google.com>
Reviewed-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm