MFC r279442,r279446:

r279442 (by rstone):

Refactor PCI resource allocation

Refactor PCI resource allocation code to allow a request for a
memory-mapped I/O window that is a multiple of a requested size.
This is needed by the SR-IOV code because the VF BARs are all
allocated contiguously. We can't just allocate a resource that is
a multiple of a single VF BAR because the size of an allocation
implies its alignment requirement.

Differential Revision: https://reviews.freebsd.org/D71
Reviewed by: jhb
Sponsored by: Sandvine Inc.

r279446 (by rstone):

Add manpages for SR-IOV enable/disable driver interface

Differential Revision: https://reviews.freebsd.org/D75
Reviewed by: wblock
Sponsored by: Sandvine Inc.