x86: crownbay: Enable graphics support

Enable graphics support on Intel Crown Bay board With the help of
vgabios for Intel TunnelCreek IGD. Tested with an external LVDS
panel connected to X4 connector and SDVO adapter connected to X9
connector on the board.

Signed-off-by: Jian Luo <jian.luo4@boschrexroth.de>
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>