bind: give path to OpenSSL when OpenSSL is enabled

bind needs to be specifically told where OpenSSL is, otherwise, the
build fails with:

checking for OpenSSL library... configure: error: OpenSSL was not found in any of /usr /usr/local /usr/local/ssl /usr/pkg /usr/sfw; use --with-openssl=/path
If you don't want OpenSSL, use --without-openssl

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>