s390/vmur: generate uevent on unsolicited device end

When a traditional channel-attached device transitions from not-ready to
ready state, an unsolicited DEVICE END I/O interrupt is raised. This
happens for example when a new file arrives in the z/VM virtual reader
device.

Change the Linux kernel to generate a change uevent when such an
interrupt occurs for any online unit record devices supported by the
vmur driver. This can be useful to automatically trigger processing of
files as they arrive in the reader device.

A sample udev rule for running a program when this event occurs looks as
follows:

  ENV{DRIVER}=="vmur", ACTION=="change", ENV{EVENT}=="unsol_de", \
    RUN{program}="/path/to/program"

The rule can be tested using the following steps:

1. Set reader device online (assuming default reader device number 000c)

   $ chzdev -ea 0.0.000c

2. Force a ready-state transition using z/VM's READY CP command

   $ vmcp ready 000c

Suggested-by: Alan Altmark <Alan_Altmark@us.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>