Include genfb in NO_DRM kernel rather than modularizing.

Modularizing required a bunch of hacks (wscons/genfb/&c. is not ready
for modules) and failed to pull in rasops dependencies, so rasops
never worked correctly.
Defer i915drm_attach_framebuffer until interrupts are running.

The i915 code initialization relies on counting hardclock ticks for a
delay (ugh).

Not an issue for modules, but it will matter when we build drm2 into
the kernel proper.
First draft of in-kernel drm2 attachment.

The drm2 `drm' device is now called `drmkms' (likewise `i915drmkms',
&c.) so that it can coexist with the old drm code to reduce diffs
from HEAD.  (Can't call a device `drm2'.)
Give drmkms its own device major so it doesn't compete with old drm.
Make i915drm_match return 6 to beat genfb_pci no matter what.
Make genfb_attach configure the wsemuldisplaydev attribute.
Make genfb replay the msgbuf only if it's becoming the console.
Make genfb a little friendlier to modules.

This is not enough to make it actually work as a module itself, but
it's enough to make the i915drm module use genfb.
Tweak genfb tweaks so they work.
Redo amd64/NO_DRM config and add amd64/DRMKMS.
Make wsdisplay_vcons likelier to be modularizable too.