Enable software-rendering by default

Fixes: QubesOS/qubes-issues#9268
For: QubesOS/qubes-core-admin-client#294
For: QubesOS/qubes-gui-agent-linux#214
(cherry picked from commit cde71d9)

vm-systemd/qubes-sysinit.sh

@@ -10,7 +10,7 @@ DEFAULT_ENABLED_NETVM="network-manager qubes-network qubes-update-check qubes-up
 DEFAULT_ENABLED_PROXYVM="qubes-network qubes-firewall qubes-update-check meminfo-writer"
 DEFAULT_ENABLED_APPVM="qubes-update-check meminfo-writer tracker evolution-data-server"
 DEFAULT_ENABLED_TEMPLATEVM="$DEFAULT_ENABLED_APPVM updates-proxy-setup"
-DEFAULT_ENABLED="meminfo-writer"
+DEFAULT_ENABLED="meminfo-writer software-rendering"
 
 # Wait for xenbus initialization
 while [ ! -e /dev/xen/xenbus ]; do