This driver attaches to the Intel VMD drive and connects a new PCI domain
starting at the max. domain, and then work down. Then existing FreeBSD
drivers will attach. Interrupt routing from the VMD MSI-X to the NVME
drive is not well known, so any interrupt is sent to all children that
register.

VROC used Intel meta data so graid(8) works with it. However, graid(8)
supports RAID 0,1,10 for read and write. I have some early code to
support writes with RAID 5. Note that RAID 5 can have life issues
with SSDs since it can cause write amplification from updating the parity
data.

Hot plug support needs a change to skip the following check to work:
if (pcib_request_feature(dev, PCI_FEATURE_HP) != 0) {
in sys/dev/pci/pci_pci.c.

Looked at by: imp, rpokala, bcr
Differential Revision: https://reviews.freebsd.org/D21383