s390/sysinfo: show partition extended name and UUID if available

Extract extended name and UUID from SYSIB 2.2.2 data.
As the code to convert the raw extended name into printable format
can be reused by stsi_2_2_2 we're moving the conversion code into a
separate function convert_ext_name.

Signed-off-by: Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>