Dumb down meminfo-writer enabling logic

Let dom0 decide whether it should be enabled or not, regardless of PCI
devices or any other factor.

Fixes QubesOS/qubes-issues#3207

vm-systemd/qubes-sysinit.sh

@@ -5,38 +5,11 @@
 . /usr/lib/qubes/init/functions
 
 # List of services enabled by default (in case of absence of qubesdb entry)
-DEFAULT_ENABLED_NETVM="network-manager qubes-network qubes-update-check qubes-updates-proxy"
-DEFAULT_ENABLED_PROXYVM="qubes-network qubes-firewall qubes-update-check"
-DEFAULT_ENABLED_APPVM="cups qubes-update-check"
+DEFAULT_ENABLED_NETVM="network-manager qubes-network qubes-update-check qubes-updates-proxy meminfo-writer"
+DEFAULT_ENABLED_PROXYVM="qubes-network qubes-firewall qubes-update-check meminfo-writer"
+DEFAULT_ENABLED_APPVM="cups qubes-update-check meminfo-writer"
 DEFAULT_ENABLED_TEMPLATEVM="$DEFAULT_ENABLED_APPVM updates-proxy-setup"
-DEFAULT_ENABLED=""
-
-# devices emulated by qemu, first list of vendor IDs then list of device IDs:
-qemu_devices="0x8086
-0x8086
-0x8086
-0x8086
-0x8086
-0x5853
-0x1013
-0x1237
-0x7000
-0x7010
-0x7020
-0x7113
-0x0001
-0x00b8
-"
-if [ -z "$(ls /sys/bus/pci/devices/)" ] || \
-        [ "$(cat /sys/bus/pci/devices/*/{vendor,device})" != "$qemu_devices" ]; then
-    # do not enable meminfo-writer (so qmemman for this domain) when any real PCI
-    # device is present
-    DEFAULT_ENABLED="$DEFAULT_ENABLED meminfo-writer"
-    DEFAULT_ENABLED_APPVM="$DEFAULT_ENABLED_APPVM meminfo-writer"
-    DEFAULT_ENABLED_PROXYVM="$DEFAULT_ENABLED_PROXYVM meminfo-writer"
-    DEFAULT_ENABLED_TEMPLATEVM="$DEFAULT_ENABLED_TEMPLATEVM meminfo-writer"
-fi
-
+DEFAULT_ENABLED="meminfo-writer"
 
 if systemd_version_changed ; then
     # Ensure we're running right version of systemd (the one started by initrd may be different)