package/apr-util: add optional support for openldap

apr-util contains optional support for openldap:

$ ls -1 output/target/usr/lib/apr-util-1/apr_ldap*
output/target/usr/lib/apr-util-1/apr_ldap-1.so
output/target/usr/lib/apr-util-1/apr_ldap.la
output/target/usr/lib/apr-util-1/apr_ldap.so

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>