[Qemu-ppc] VGA cirrus patch prevents video output

[Programmingkid]

I noticed that the video in QEMU stopped working. When I start qemu-system-ppc 
all I see is a black window. Not even OpenBIOS displays anything. After some 
bisecting I found out it was this patch that causes the problem: 

Commit 29f9cef39eb1ae55e82c6763eb22d7a1bdff7276
Author: Sebastian Bauer <address@hidden>
Date:   Mon Jul 2 21:13:45 2018 +0200

    ppc: Include vga cirrus card into the compiling process
    
    Drivers for this card exists on PPC-based AmigaOS guests so it is useful to
    allow users to emulate the graphics card for PPC machines.
    
    As cirrus vga is currently preferred over std(vga) in absence of any user
    choice, this change also sets the default display of spapr machines to
    std as otherwise qemu refuses to start these machines. Not specifying an
    explicit graphics mode is for instance done by 'make check'.
    
    Signed-off-by: Sebastian Bauer <address@hidden>
    Signed-off-by: David Gibson <address@hidden>


I think a solution to this problem might be to have the mac99 machine use "-vga 
std" as default. When I use -vga std, video works again.