Use GEM in modesetting

Use GEM for ring buffer setup and framebuffer allocation.  This means reworking
the hardware status page stuff a bit (just use the basic range allocator for
vram for now) and #ifdef'ing out the TTM & DRI2 code.  Works well enough to
load/unload several times and display fbcon on my T61 (though there's still
some unexplained console corruption).