s390/zcrypt: Rework CONFIG_ZCRYPT Kconfig text.

The CONFIG_ZCRYPT Kconfig entry in drivers/crypto showed
outdated hardware whereas the latest cards where missing.
Reworked the text to reflect the current abilities of the
zcrypt device driver.

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