Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Merge from vmobj-rwlock branch:
Remove unused inclusion of vm/vm_pager.h and vm/vnode_pager.h.

Sponsored by: EMC / Isilon storage division
Tested by: pho
Reviewed by: alc

Remove platform APIs which are not used by any code and which had only stub
implementations or no implementation on all platforms.

Some of these functions might be good ideas, but their semantics were unclear
given the lack of implementation, and an unlucky porter could be fooled into
trying to implement them or, worse, being baffled when something like
platform_trap_enter() failed to be called.

- dump_avail layout should be sequence of [start, end)
pairs, not <start, size>.

Spotted by: alc@

- Populate dump_avail with proper values from phys_avail

- Call post-boot fixup function in order to get proper static
symbols resolving in DDB
- When zeroing .bss/.sbss do not round end address to page boundary,
it's not neccessary and might destroy data pased by trampoline or
boot loader

Update from old DDB convetion to initialize debugger to new KDB way.
Always call kdb_init(). If we have KDB enabled, then provide a handy
place to break to the debugger.

Merge from projects/mips to head by hand:

Merge support for very early alchemy port. I wouldn't merge this
except I don't want it to get lost when we retire projects/mips.
Should be consiered pre-alpha at this stage. Also, alchemy is now
owned by rmi, but started out life as a separate processor line, so
I'm leaving it in its own directory rather than try to shoe-horn it
into the unrelated rmi directory. Its future location is an open
question.

Rename mips_pcpu_init to mips_pcpu0_init since it applies only to the
BSP. Provide a missing prototype.

Centralize initialization of pcpu, and set curthread early...

With this commit our friend RMI will now compile. I have
not tested it and the chances of it running yet are about
ZERO.. but it will now compile. The hard part now begins,
making it run ;-)

- Revert changes accidentally killed by merge operation

First milestone on Alchemy port: Simplest kernel now compiles.