default devices: vga adapter.

default devices: vga adapter.

Qemu creates a vga display for you in case you didn't specify one on the
command line.  Right now this is tied to the '-vga <type>' command line
switch, which in turn causes trouble if you are creating your gfx card
using '-device VGA,<props>'.

This patch adds a variable default_vga which says whenever a default
serial line should be added.  It is enabled by default.  It is cleared
when qemu finds '-vga' or '-device {VGA,Cirrus VGA,QEMUware SVGA}' on
the command line.

'-device VGA' still doesn't work though due to a initialization order
issue (vga must init before calling i440fx_init_memory_mappings).

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
(cherry picked from commit 64465297cd4c701942988f36f7ce707fb21cc1d8)