cpi: Disable CPI for SEL guests by default

The cpictl utility sends control-program identification data
from protected virtualization guests to hosts by default.
This behaviour leaks the below potentially sensitive
information to untrusted hosts.
- system_type
- system_level
- sysplex_name
- system_name

To prevent this behaviour, enhance the cpictl utility to stop
setting CPI information on protected virtualization guests by
default. If the user chooses to set the CPI information, it
could be set by one of the below options
- use the command line option --permit-cpi
- set the environment variable CPI_PERMIT_ON_PVGUEST to 1 to
control the CPI service behaviour during boot

Signed-off-by: Hendrik Brueckner <brueckner@linux.ibm.com>
Signed-off-by: Shalini Chellathurai Saroja <shalini@linux.ibm.com>
Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Reviewed-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

etc/sysconfig/cpi

@@ -18,3 +18,17 @@ CPI_SYSTEM_NAME=""
 # CPI sysplex name
 #
 CPI_SYSPLEX_NAME=""
+
+#
+# CPI permit on protected virtualization guests
+#
+# Important: Set CPI_PERMIT_ON_PVGUEST=1 only if you trust the host system.
+# Enabling these options allows the host to receive potentially sensitive
+# Control-Program Identification (CPI) data from the protected virtualization
+# guest, including:
+# - system_type
+# - system_level
+# - sysplex_name
+# - system_name
+#
+CPI_PERMIT_ON_PVGUEST=