drm/bochs: Implement nomodeset

Up until now, the bochsdrm driver didn't handle the nomodeset option
at boot, and didn't provide a "modeset" module option either.

This patch implements both.

The new parameter can be used by specifying bochs-drm.modeset=0
at boot time.

Signed-off-by: Max Staudt <mstaudt@suse.de>
Link: http://patchwork.freedesktop.org/patch/msgid/1484763012-17783-1-git-send-email-mstaudt@suse.de


Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>