s390/uaccess: rename/sort labels in inline assemblies

Rename and sort labels in uaccess inline assemblies to increase
readability. In addition have only one EX_TABLE entry per line - also to
increase readability.

Except for debug sections the output of "objdump -Dr" of the uaccess object
file is identical before/after this change.

Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>