drm/bochs: Drop fake gamma support

Only really needed for fbdev emulation at 8bpp. And bochs doesn't do
that. And either way bochs only does 32bit rgb, so this is all pretty
much wasted dead code.

The only consideration is that we need to not set up any gamma size
either.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Dave Airlie <airlied@redhat.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1459331485-28376-5-git-send-email-daniel.vetter@ffwll.ch