video: Update video_set_default_colors() to support invert

It is useful to be able to invert the colours in some cases so that the
text matches the background colour. Add a parameter to the function to
support this.

It is strange that function takes a private data structure from another
driver as an argument. It seems better to pass the device and have the
function internally work out how to find its required information.

Signed-off-by: Simon Glass <sjg@chromium.org>