remove bgr (Stefano Stabellini)

remove bgr (Stefano Stabellini)

Do not handle bgr host displays in the backends.

Right now a bgr flag exists so that sdl can set it, if the SDL_Surface
is bgr.
Afterwards the graphic device (e.g. vga.c) does the needed conversion.

With this patch series is sdl that is responsible for rendering the format
provided by the graphic device that must provide a DisplaySurface
(ds->surface) in 16 or 32 bpp, rgb.
Afterwards sdl creates a SDL_Surface from the given DisplaySurface and
blits it into the main SDL_Surface using SDL_BlitSurface.

Everything is handled by sdl transparently, because SDL_BlitSurface is
perfectly capable of handling bgr displays by itself.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Patch adapted for qemu-xen-unstable by Stefano Stabellini.
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>