Add a bootloader for octeon.

The firmware on OCTEON machines usually does not provide an interface
for accessing devices, which has made it tricky to implement an OpenBSD
bootloader. To solve this device access problem, this new loader has
been built on top of a small kernel. The kernel provides all the
necessary devices drivers, while most of the usual bootloader logic
is in a userspace program in a ramdisk.
The loader program is accompanied by a special device, octboot(4).
The main purpose of this device is to implement a mechanism for
loading and launching kernels. The mechanism has been inspired by Linux'
kexec(2) system call.
The bootloader will be enabled later when it is ready for general use.
Discussed with deraadt@

src/etc/etc.octeon/MAKEDEV.md

@@ -1,6 +1,6 @@
 define(MACHINE,octeon)dnl
 vers(__file__,
-	{-$OpenBSD: MAKEDEV.md,v 1.13 2016/09/04 15:38:59 naddy Exp $-},
+	{-$OpenBSD: MAKEDEV.md,v 1.14 2019/07/17 14:36:31 visa Exp $-},
 etc.MACHINE)dnl
 dnl
 dnl Copyright (c) 2001-2006 Todd T. Fries <todd@OpenBSD.org>
@@ -86,6 +86,10 @@ _DEV(switch, 75)
 dnl
 divert(__mddivert)dnl
 dnl
+boot)
+	_recurse ramdisk random
+	M octboot	c 21 0 600
+	;;
 _std(2, 3, 35, 6)
 	M openprom	c 20 0 600
 	;;