[qemu] Initialize vga from within qemu for when the bios doesn't do so.

[qemu] Initialize vga from within qemu for when the bios doesn't do so.
On xen/x86, vga bios is copied to 0xC0000 by guest firmware.
However on ia64 platform, native firmware depends on some
initialization vga state at power on and so does guest firmware.
That's why that vga bios initialization stub is required for vti
domain, to match platform requirement.

Signed-off-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Zhang Xiantao <xiantao.zhang@intel.com>
Signed-off-by: Christian Limpach <Christian.Limpach@xensource.com>