radeondrmkms on i386. the problem is that the pcdisplay@isa
and vga@isa drivers rely on some other driver having already
mapped the vga registers to know they should not attach, but
radeondrmkms attaches late as it needs rootfs access, and it
does not map these registers, and either of vga or pcdisplay
will attach, and then attach wsdisplay0, and then getty and
X11 will fail and you shake a tiny fist at the computer.
so, for i386, map and unmap the VGA register space between
the normal attach and the mountroot attach.
ae839ccccc