powerpc/pseries: Log hcall return codes for PLPKS debug

The plpks code converts hypervisor return codes into their Linux
equivalents so that users can understand them.  Having access to the
original return codes is really useful for debugging, so add a
pr_debug() so we don't lose information from the conversion.

Signed-off-by: Russell Currey <ruscur@russell.cc>
Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230210080401.345462-19-ajd@linux.ibm.com