Add "dbm" packageconfig to enable legacy dbm support in libdb. This support is
needed to build libpam pam_userdb.so plugin.
(From OE-Core rev: 841573cea6d06dcba45227a8126153b0629b1b0c)
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>