s390/mm,fault: improve readability by using teid union

Get rid of some magic numbers, and use the teid union and also some
ptrace PSW defines to improve readability.

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>