display/stdvga: add edid support.

display/stdvga: add edid support.

This patch adds edid support to the qemu stdvga.  It is turned off by
default and can be enabled with the new edid property.  The patch also
adds xres and yres properties to specify the video mode you want the
guest use.  Works only with edid enabled and updated guest driver.

The mmio bar of the stdvga has some unused address space at the start.
It was reserved just in case it'll be needed for virtio, but it turned
out to not be needed for that.  So let's use that region to place the
EDID data block there.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 20180925075646.25114-6-kraxel@redhat.com