pimd: add do_install to pimd

The previous do_install is empty and do nothing.

Unset variables datadir and mandir, use pimd's default set.
So it could install doc files correctly.

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>