s390/zcrypt: Convert to PM ops

Switch the zcrypt bus from legacy suspend/resume callbacks to dev_pm_ops.
The conversion is straight forward with the help of SIMPLE_DEV_PM_OPS().
The new dev_pm_ops based version is functionally equivalent to the legacy
callbacks version.

This will allow to eventually remove support for legacy suspend/resume
callbacks from the kernel altogether.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Harald Freudenberger <freude@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>