s390/pkey: Load pkey kernel module automatically

With the recent enhancements of the pkey kernel module,
the pkey kernel module should be loaded automatically
during system startup, if MSA is available.

When used for swap device encryption with random protected
keys, pkey must be loaded before /etc/crypttab is processed,
otherwise the sysfs attributes to read the key from are
not available.

Signed-off-by: Ingo Franzki <ifranzki@linux.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.ibm.com>
Reviewed-by: Harald Freudenberger <freude@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>