getty: Start getty on 3270 terminals available on Linux on System z

getty: Start getty on 3270 terminals available on Linux on System z

Add the first 3270 terminal device that is associated with the Linux preferred
console to the list of virtualization consoles.  This is required to
automatically start a getty if the conmode=3270 kernel parameter is specified
for Linux on z/VM instances.  Note that a queued upstream patch also enable
the 3270 terminal device if it is associated with the Linux preferred console.
How

To successfully start agetty on a 3270 terminal, a change in the agetty
parameter order is required.  Previously, agetty would started like this:

    /sbin/agetty --keep-baud 3270/tty1 115200,38400,9600 TERM

The agetty program interprets the "3270/tty1" as baud rate and fails to start
with the "bad speed: 3270/tty1" error message.  Fixing this in agetty is more
complex rather than reordering the command line parameters like this:

    /sbin/agetty --keep-baud 115200,38400,9600 3270/tty1 TERM

According to agetty sources and "agetty --help", agetty accepts the "tty",
"baudrate tty", and "tty baudrate" specifications.

P.S. The "tty: Set correct tty name in 'active' sysfs attribute" introduces
     a change to display the terminal device which is associated with the
     Linux preferred console.  This change helps to let systemd handle this
     particular case only.  Without the changes of this commit, no additional
     3270 terminal device can be managed by systemd.

     https://git.kernel.org/cgit/linux/kernel/git/gregkh/tty.git/commit/?id=723abd87f6e536f1353c8f64f621520bc29523a3