Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

- Search the whole OFW device tree instead of only the children of the
root nexus device for the CPUs as starting with UltraSPARC IV the 'cpu'
nodes hang off of from 'cmp' (chip multi-threading processor) or 'core'
or combinations thereof. Also in large UltraSPARC III based machines
the 'cpu' nodes hang off of 'ssm' (scalable shared memory) nodes which
group snooping-coherency domains together instead of directly from the
nexus.
It would be great if we could use newbus to deal with the different ways
the 'cpu' devices can hang off of pseudo ones but unfortunately both
cpu_mp_setmaxid() and sparc64_init() have to work prior to regular device
probing.
- Add support for UltraSPARC IV and IV+ CPUs. Due to the fact that these
are multi-core each CPU has two Fireplane config registers and thus the
module/target ID has to be determined differently so the one specific
to a certain core is used. Similarly, starting with UltraSPARC IV the
individual cores use a different property in the OFW device tree to
indicate the CPU/core ID as it no longer is in coincidence with the
shared slot/socket ID.
This involves changing the MD KTR code to not directly read the UPA
module ID either. We use the MID stored in the per-CPU data instead of
calling cpu_get_mid() as a replacement in order prevent clobbering any
registers as side-effect in the assembler version. This requires CATR()
invocations from mp_startup() prior to mapping the per-CPU pages to be
removed though.
While at it additionally distinguish between CPUs with Fireplane and
JBus interconnects as these also use slightly different sizes for the
JBus/agent/module/target IDs.
- Make sparc64_shutdown_final() static as it's not used outside of
machdep.c.

Lower UPA_MEMSTART to 0x1c000000000. This is required for some larger
Enterprise machines.

Add support for starting secondary cpus in kernel, as opposed to relying
on the loader to do it. Improve smp startup code to be less racy and to
defer certain things until the right time. This almost boots single user
on my dual ultra 60, it is still very fragile:

SMP: AP CPU #1 Launched!
Enter full pathname of shell or RETURN for /bin/sh:
# ls
Debugger("trapsig")
Stopped at Debugger+0x1c: ta %xcc, 1
db> heh
No such command
db>

Add macros to extract the UPA module id from the UPA config register.
This is the hardware cpuid.

Add upa.h, which I had previously forgotten, to unbreak the sparc64
kernel build.

Pointy hat to: tmm