[S390] cio: introduce consistent subchannel scanning

Previously, there were multiple subchannel scanning mechanisms
which could potentially conflict with each other. Fix this problem
by moving blacklist and ccw driver triggered scanning to the
existing evaluation method.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>