Implement interface to create SR-IOV Virtual Functions

Implement interface to create SR-IOV Virtual Functions

Implement the interace to create SR-IOV Virtual Functions (VFs).
When a driver registers that they support SR-IOV by calling
pci_setup_iov(), the SR-IOV code creates a new node in /dev/iov
for that device.  An ioctl can be invoked on that device to
create VFs and have the driver initialize them.

At this point, allocating memory I/O windows (BARs) is not
supported.

Differential Revision:	https://reviews.freebsd.org/D76
Reviewed by:		jhb
MFC after: 		1 month
Sponsored by:		Sandvine Inc.