s390/ctlreg: allow to call system_ctl_set/clear_bit() early

s390/ctlreg: allow to call system_ctl_set/clear_bit() early

Allow to call system_ctl_set_bit() and system_clt_clear_bit() early, so
that users do not have to take care when the control register save area
has been initialized. Users are supposed to use system_ctl_set_bit() and
system:clt_clear_bit() for all control register changes which are supposed
to be seen globally.

Depending on the system state such calls will change:

- local control register contents
- save area and local control register contents
- save area and global control register contents

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