drm/bochs: add edid support.

Recent qemu (latest master branch, upcoming 3.1 release) got support
for EDID data.  This patch adds guest driver support.

EDID support in qemu is not (yet) enabled by default, so please use
'qemu -device VGA,edid=on' for testing.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20181029205048.13200-1-kraxel@redhat.com