vfio-pci: Fix BAR size overflow

We use an unsigned int when working with the PCI BAR size, which can
obviously overflow if the BAR is 4GB or larger.  This needs to change
to a fixed length uint64_t.  A similar issue is possible, though even
more unlikely, when mapping the region above an MSI-X table.  The
start of the MSI-X vector table must be below 4GB, but the end, and
therefore the start of the next mapping region, could still land at
4GB.

Suggested-by: Nishank Trivedi <nishank.trivedi@netapp.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Don Slutz <dslutz@verizon.com>
Tested-by: Alexey Kardashevskiy <aik@ozlabs.ru>
