s390/cio: generate delayed uevent for vfio-ccw subchannels

s390/cio: generate delayed uevent for vfio-ccw subchannels

[ Upstream commit 2bc55eaeb88d30accfc1b6ac2708d4e4b81ca260 ]

The common I/O layer delays the ADD uevent for subchannels and
delegates generating this uevent to the individual subchannel
drivers. The vfio-ccw I/O subchannel driver, however, did not
do that, and will not generate an ADD uevent for subchannels
that had not been bound to a different driver (or none at all,
which also triggers the uevent).

Generate the ADD uevent at the end of the probe function if
uevents were still suppressed for the device.

Message-Id: <20200327124503.9794-3-cohuck@redhat.com>
Fixes: 63f1934d562d ("vfio: ccw: basic implementation for vfio_ccw driver")
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>