MFC: 319690

MFC: 319690

r319690
	hyperv/pcib: use the device serial number as PCI domain

	Currently the PCI domain is initialized with the instance GUID in
	vmbus_pcib_attach(). It turns out the GUID can change across VM reboot,
	while some users want a persistent value for PCI domain. The solution is
	that we can change to use the device serial number, which starts with 1
	and is unique within a VM.

	Obtained from:	Haiyang Zhang
	Sponsored by:	Microsoft

git-svn-id: svn://svn.freebsd.org/base/stable/10@319941 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f