rules: Limit the number of device units generated for serial ttys

As per the suggestion in systemd/systemd#33242.

This reduces the number of /dev/ttySXX device units generated in
mkosi from 32 to 4.

(cherry picked from commit dc38f9a)
(cherry picked from commit a3d9433)
(cherry picked from commit 6391242)
(cherry picked from commit 1a8549f)
(cherry picked from commit 38f11f4)

Author: DaanDeMeyer

rules.d/99-systemd.rules.in

@@ -10,6 +10,8 @@
 ACTION=="remove", GOTO="systemd_end"
 
 SUBSYSTEM=="tty", KERNEL=="tty[a-zA-Z]*|hvc*|xvc*|hvsi*|ttysclp*|sclp_line*|3270/tty[0-9]*", TAG+="systemd"
+# Exclude 8250 serial ports with a zero IO port, as they are not usable until "setserial /dev/ttySxxx port …" is invoked.
+SUBSYSTEM=="tty", KERNEL=="ttyS*", DRIVERS=="serial8250", ATTR{port}=="0x0", ENV{SYSTEMD_READY}="0"
 KERNEL=="vport*", TAG+="systemd"
 
 SUBSYSTEM=="ptp", TAG+="systemd"