spice: require spice-protocol >= 0.8.1

Requiring spice-server >= 0.8.2 is not enough since spice-server.pc
doesn't require spice-protocol (any version). Until that is fixed
upstream an explicit requirement in qemu fixes compilation broken since

commit 2e1a98c9
Author: Alon Levy <alevy@redhat.com>
Date:   Fri Feb 24 23:19:30 2012 +0200

    qxl: introduce QXLCookie
Reported-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NAlon Levy <alevy@redhat.com>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

configure

@@ -2592,6 +2592,7 @@ EOF
   spice_cflags=$($pkg_config --cflags spice-protocol spice-server 2>/dev/null)
   spice_libs=$($pkg_config --libs spice-protocol spice-server 2>/dev/null)
   if $pkg_config --atleast-version=0.8.2 spice-server >/dev/null 2>&1 && \
+     $pkg_config --atleast-version=0.8.1 spice-protocol > /dev/null 2>&1 && \
      compile_prog "$spice_cflags" "$spice_libs" ; then
     spice="yes"
     libs_softmmu="$libs_softmmu $spice_libs"