patch for topology detection of Intel CPUs

[Reposted from stable_at_; edited]

The below patch is against sources in FreeBSD tree, it should be applied
either to sys/amd64/amd64/mp_machdep.c or sys/i386/i386/mp_machdep.c depending
on the desired architecture:
http://people.freebsd.org/~avg/intel-cpu-topo.diff

The patch is substantially based on the Junk-uk's patch, but with some changes
and additions:
- topo_prob_0x4() is rewritten so that it does APIC ID matching against masks
as described in the Intel article.  The code still heavily depends on the
assumption of the uniform topology, it discovers number of cores in BSP package
and number of threads in BSP core and extrapolates that to global topology.
The difference with current code and Junk-uk's patch is that actual APIC ID
matching is done as opposed to deriving counts purely from max. values.

- topo_prob_0x4() is invoked for 1 <= cpu_high < 4 case as well as for 4 <=
cpu_high < 11 case as done in the current code, but unlike Junk-uk's patch.  The
code should be able to properly handle that class of CPUs and either detect
hyperthreading topology or fallback to one processor per package topology.

- added a few comments that describe uniformity assumption, plus couple other
useful things.

- changed "final fallback" code, so that each logical CPU is considered to be in
its own physical package as opposed to current code placing all logical CPUs as
cores of a single package.

The rest is Junk-uk's work.

Concerns:
- about my code: ilog2_round_pow2 name is ugly; looking for suggestions on a
better name or re-arranging/writing that code, so that the function is not needed.
- about current code: logical_cpus variable (don't confuse with cpu_logical)
doesn't seem to be consistently used; e.g. it is not set at all by
topo_probo_0xb(); also, the method of using it for setting logical_cpus_mask
doesn't seem to be reliable - BSP may be missed.

Reviews, comments and test reports are very welcome!
Please test the patch if you have any problems with how CPU topology is reported
by the current code.  Please test even if everything is OK, to avoid regressions.

Thanks!
-- 
Andriy Gapon