Currently on s390 the check for live dumps is called in s390x_init(POST_INIT).
Unfortunately this code is not executed when the "--minimal" command line
option is specified. Therefore when using this option, "help -p" does not
show the correct information for flags2.
This patch moves the s390x_check_live() invoctation to s390x_init(PRE_GDB),
that is called also for --minimal.