Sync up with the files in the hammer branch in the p4 tree to get basic
AMD64 support.  There is still more to add.
Lock accesses to the vm_object's ref_count and resident_page_count.
 - Update the vm_object locking in vm_object_reference().
 - Convert some dead code in vm_object_reference() into a comment.
Slight reorg and added AMD64 support.  A couple of the MODINFOMD_* values
that were added to sparc64 and later powerpc, really should have been in
the MI area.  But changing that now with insufficient preperation will
just cause too much pain.

Move MD_FETCH() to the MI sys/linker.h file to avoid another two copies
of it.
Back out last commits.  The elf64/elf32 kernel name thing was more pain
than it was worth.
Fix printf warning caused by recent CAM change.
<b30> is 'IA64' - ie: you're running on an ia64 in 32 bit mode.
Hack to enable getting two different elf32 and elf64 loaders in the
same i386 loader binary.
Lock an update to a vm_object's ref_count.
Enable the i386 loader to load and run an amd64 kernel.  If this puts
things over floppy size limits, I can exclude it for release builds or
something like that.  Most of the changes are to get the load_elf.c file
into a seperate elf32_ or elf64_ namespace so that you can have two
ELF loaders present at once.  Note that for 64 bit kernels, it actually
starts up the kernel already in 64 bit mode with paging enabled.  This
is really easy because we have a known minimum feature set.

Of note is that for amd64, we have to pass in the bios int 15 0xe821
memory map because once in long mode, you absolutely cannot make VM86
calls.  amd64 does not use 'struct bootinfo' at all.  It is a pure loader
metadata startup, just like sparc64 and powerpc.  Much of the
infrastructure to support this was adapted from sparc64.
Nuke; repocopied to elf32_freebsd.c where it lives on.
I changed the numbering of the MODINFOMD_SMAP during the commit, so
recognize the old number for my development boxes so I can use old
loader/pxeboot for a while if I need to.
Update the hardcoded bus tags for early console support for amd64.
Add AMD64 support to dev/fb.  It isn't optimized.
Only use the pc bios stuff on i386's.  I think this might even be unused
there too.
Argh.  This was broken by the last-minute elf32/elf64/"elf kernel" changes.
Commit a missed change to keep in sync with the MI elf loader.
Extend the scope of the vm_object locking in vm_object_split().
Fix compile errors on ia64 in dagetcapacity.  Set block_len and maxsector
to 0 initially.  It seems that the ia64 backend isn't as "smart" as the
i386 backend, which realized that those variables were only set or used
when error == 0, and thus were not used uninitialized.
Relax the test for when to use LBA instead of CHS size.