drm/bochs: new driver

DRM driver for (virtual) vga cards using the bochs dispi
interface, such as the qemu standard vga (qemu -vga std).

Don't bother supporting anything but 32bpp for now, even
though the virtual hardware is able to do that.

Known issue: mmap(/dev/fb0) doesn't work.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>