s390: add ELF note type for encrypted CPU state of a PV VCPU

s390: add ELF note type for encrypted CPU state of a PV VCPU

The type NT_S390_PV_CPU_DATA note contains the encrypted CPU state of
a PV VCPU. It's only relevant in dumps of s390 PV VMs and can't be
decrypted without a second block of encrypted data which provides key
parts. Therefore we only reserve the note type here.

The zgetdump tool from the s390-tools package can, together with a
Customer Communication Key, be used to convert a PV VM dump into a
normal VM dump. zgetdump will decrypt the CPU data and overwrite the
other respective notes to make the data accessible for crash and other
debugging tools.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
[agordeev@linux.ibm.com changed desctiption]
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>