s390x: lib: add teid union and clear teid from lowcore

Add a union to represent Translation-Exception Identification (TEID).

Clear the TEID in expect_pgm_int clear_pgm_int.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Message-Id: <20210611140705.553307-6-imbrenda@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>