s390/time: introduce new store_tod_clock_ext()

Introduce new store_tod_clock_ext() function, which is the same like
store_tod_clock_ext_cc() except that it doesn't return a condition
code.

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