x86: dm: video: Add a framebuffer driver that utilizes VBT

When a VBT is given to an FSP that supports graphics initialization,
the FSP will produce a graphics info HOB that contains all necessary
information for the linear frame buffer of the integrated graphics
device. This adds a DM video driver for it.

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