x86: broadwell: Add video support

Add a video driver for Intel's broadwell integrated graphics controller.
This uses a binary blob for most init, with the driver just performing a few
basic tasks.

This driver supports VESA as the mode-setting mechanism. Since most boards
don't support driver model yet with VESA, a special case is added to the
Kconfig for broadwell. Eventually all boards will use driver model and this
can be removed.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Bin Meng <bmeng.cn@gmail.com>