s390/dasd: Prepare for additional path event handling

[ Upstream commit b72949328869dfd45f6452c2410647afd7db5f1a ]

As more path events need to be handled for ECKD the current path
verification infrastructure can be reused. Rename all path verifcation
code to fit the more broadly based task of path event handling and put
the path verification in a new separate function.

Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Reviewed-by: Stefan Haberland <sth@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Stable-dep-of: 460e9bed82e4 ("s390/dasd: Fix potential memleak in dasd_eckd_init()")
Signed-off-by: Sasha Levin <sashal@kernel.org>