spice: add qxl device

spice: add qxl device

qxl is a paravirtual graphics card.  The qxl device is the bridge
between the guest and the spice server (aka libspice-server).  The
spice server will send the rendering commands to the spice client, which
will actually render them.

The spice server is also able to render locally, which is done in case
the guest wants read something from video memory.  Local rendering is
also used to support display over vnc and sdl.

qxl is activated using "-vga qxl".  qxl supports multihead, additional
cards can be added via '-device qxl".

[ v2: add copyright to files                     ]
[ v2: use qemu-common.h for standard includes    ]
[ v2: create separate qxl-vga device for primary ]

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