s390/zcrypt: introduce ctfm field in struct CPRBX

Modify the CPRBX struct to expose a new field ctfm for use with hardware
command filtering within a CEX8 crypto card in CCA coprocessor mode.

The field replaces a reserved byte padding field so that the layout of the
struct and the size does not change.

The new field is used only by user space applications which may use this to
expose the HW filtering facilities in the crypto firmware layers.

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