s390/uv: add prot virt guest/host indication files

Let's export the prot_virt_guest and prot_virt_host variables into the
UV sysfs firmware interface to make them easily consumable by
administrators.

prot_virt_host being 1 indicates that we did the UV
initialization (opt-in)

prot_virt_guest being 1 indicates that the UV indicates the share and
unshare ultravisor calls which is an indication that we are running as
a protected guest.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>