libkmod: modinfo: implement line splitting in hex_to_str
libkmod: modinfo: implement line splitting in hex_to_str

The key output is usually short, but for signature it is more
readable to output it in several lines.

Implement line splitting. Set line limit hardcoded to 20 hex
numbers (not characters).

Signed-off-by: Yauheni Kaliuta <0d6c66cf06ee77089f9b834ad16e0f050cf87c60@redhat.com>

pmmccorm/kmod,pmmccorm/kmod,lucasdemarchi/kmod,lucasdemarchi/kmod,pmmccorm/kmod,lucasdemarchi/kmod