Add a new helper function umove_ulong_array_or_printaddr

Add a new helper function umove_ulong_array_or_printaddr

* defs.h (umove_ulong_array_or_printaddr): New prototype.
* util.c (umove_ulong_array_or_printaddr): New function.
* desc.c (sys_pselect6): Use it instead of open-coding
a proxy struct parser for different personalities.
* io.c (tprint_iov_upto): Use it instead of open-coding
a struct iovec parser for different personalities.
* kexec.c (print_kexec_segments): Use it instead of open-coding
a struct kexec_segment parser for different personalities.
(print_seg): Pass arguments using an array.