configure: qemu-ga: report MSI install support in summary

Currently we need to examine config-host.mak to determine whether
options/probes for MSI package generation had desired result. Report
this more prominently in ./configure summary as we do with other
guest agent configure options.
Reviewed-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

configure

@@ -4577,6 +4577,7 @@ echo "libnfs support    $libnfs"
 echo "build guest agent $guest_agent"
 echo "QGA VSS support   $guest_agent_with_vss"
 echo "QGA w32 disk info $guest_agent_ntddscsi"
+echo "QGA MSI support   $guest_agent_msi"
 echo "seccomp support   $seccomp"
 echo "coroutine backend $coroutine"
 echo "coroutine pool    $coroutine_pool"