spice: raise requirement to 0.12

spice: raise requirement to 0.12

With the next qemu version (1.3) we are going to bump the qxl device
revision to 4.  The new features available require a recent spice-server
version, so raise up the bar.  Otherwise we would end up with different
qxl revisions depending on the spice-server version installed, which
would be a major PITA when it comes to compat properties.

Clear out a big bunch of #ifdefs which are not needed any more.

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