s390/pkey: Introduce new API for secure key verification

User space needs some information about the secure key(s)
before actually invoking the pkey and/or paes funcionality.
This patch introduces a new ioctl API and in kernel API to
verify the the secure key blob and give back some
information about the key (type, bitsize, old MKVP).
Both APIs are described in detail in the header files
arch/s390/include/asm/pkey.h and arch/s390/include/uapi/asm/pkey.h.

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