console: stop using PixelFormat

console: stop using PixelFormat

With this patch the qemu console core stops using PixelFormat and pixman
format codes side-by-side, pixman format code is the primary way to
specify the DisplaySurface format:

 * DisplaySurface stops carrying a PixelFormat field.
 * qemu_create_displaysurface_from() expects a pixman format now.

Functions to convert PixelFormat to pixman_format_code_t (and back)
exist for those who still use PixelFormat.   As PixelFormat allows
easy access to masks and shifts it will probably continue to exist.

[ xenfb added by Benjamin Herrenschmidt ]

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>