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

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

Fix the frambuffer issues by calling pmap_mapdev() in the attach routine. This
will make the framebuffer region uncacheable and it will create a proper
KVA -> RAM mapping.

Initial support for running FreeBSD on the Nintendo Wii. We're able to
reach single user mode using a memory disk device as the file system.

This port includes the framebuffer driver, the PIC driver, a platform
driver and the GPIO driver. The IPC driver (to talk to IOS kernels) is
not yet written but there's a placeholder for it.

There are still some MMU problems and to get a working system you need to
patch locore32.S. Since we haven't found the best way yet to address that
problem, we're not committing those changes yet. The problem is related to
the different BAT layout on the Wii and to the fact that the Homebrew
loader doesn't clean up the special registers (including the 8 BATs)
before passing control to us.

You'll need a Wii with Homebrew loader and a TV that can do NTSC (for now).

Submitted by: Margarida Gouveia