The architecture supports masks of variable length for sclp write
event mask. We currently only support 4 byte event masks, as that
is what Linux uses.

Let's extend this to the maximum mask length supported by the
architecture and return 0 to the guest for the mask bits we don't
support in core.

Initial patch by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: NJason J. Herne <jjherne@linux.vnet.ibm.com>
Message-Id: <1507729193-9747-1-git-send-email-jjherne@linux.vnet.ibm.com>
Acked-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: NCornelia Huck <cohuck@redhat.com>