s390/zcrypt: remove ZCRYPT_MULTIDEVNODES kernel config option

Remove ZCRYPT_MULTIDEVNODES kernel config option and make
the dependent code always build.

The last years showed, that this option is enabled on all distros
and exploited by some features (for example CEX plugin for kubernetes).
So remove this choice as it was never used to switch off the multiple
devices support for the zcrypt device driver.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Holger Dengler <dengler@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>