ssmping: add do_install to ssmping

The previous do_install is empty and do nothing.

Tweak install doc dir, so the man doc could be installed to /usr/share/man
rather than /usr/locale/man.

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>