Add a jail parameter, allow.kmem, which lets jailed processes access
/dev/kmem and related devices (i.e. grants PRIV_IO and PRIV_KMEM_WRITE).
This in conjunction with changing the drm driver's permission check from
PRIV_DRIVER to PRIV_KMEM_WRITE will allow a jailed Xorg server.

Submitted by:	netchild
MFC after:	1 week
Add libexecinfo.

MFC after:	3 days
Enhance the support for PCI legacy INTx interrupts and enable them in
the virtio backends.
- Add a new ioctl to export the count of pins on the I/O APIC from vmm
  to the hypervisor.
- Use pins on the I/O APIC >= 16 for PCI interrupts leaving 0-15 for
  ISA interrupts.
- Populate the MP Table with I/O interrupt entries for any PCI INTx
  interrupts.
- Create a _PRT table under the PCI root bridge in ACPI to route any
  PCI INTx interrupts appropriately.
- Track which INTx interrupts are in use per-slot so that functions
  that share a slot attempt to distribute their INTx interrupts across
  the four available pins.
- Implicitly mask INTx interrupts if either MSI or MSI-X is enabled
  and when the INTx DIS bit is set in a function's PCI command register.
  Either assert or deassert the associated I/O APIC pin when the
  state of one of those conditions changes.
- Add INTx support to the virtio backends.
- Always advertise the MSI capability in the virtio backends.

Submitted by:	neel (7)
Reviewed by:	neel
MFC after:	2 weeks
Micro-optimize 8-bit blanking.  This is the same as in ofw_syscons.

Reviewed by:	ray
MFC after:	1 week
Fix the ordering of the arguments to printf in
uhub_child_location_string(). This produced bogus information in

	dev.<USB driver>.<id>.%location

output from sysctl.

MFC after:	2 weeks
Ressurect the local change documenting
authpf's requirement for a mounted fdescfs(5).

PR:		docs/186250
MFC after:	1 week
[automated] Merge in upstream-github/master