s390/zcrypt: provide cex4 cca sysfs attributes for cex3

This patch introduces the sysfs attributes serialnr and
mkvps for cex2c and cex3c cards. These sysfs attributes
are available for cex4c and higher since
commit 7c4e91c0 ("s390/zcrypt: new sysfs attributes serialnr and mkvps")'
and this patch now provides the same for the older cex2
and cex3 cards.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>