db: do not install db_verify if 'verify' is not enabled

On target, when running `db_verify /var/lib/rpm/Packages', we get
the following error.

  db_verify: BDB0571 library build did not include support for database verification

This is because db_verify is installed but 'verify' PACKAGECONFIG is
not enabled. So fix it by not installing do_verify in such case.

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit b5ffdb29)
Signed-off-by: Steve Sakoman <steve@sakoman.com>