package/bind: reorder openssl variables

openssl is mandatory since bump to version 9.16.26 in commit
8adeaec8 so move openssl variables in
the beginning of bind.mk instead of keeping them in the middle of the
file. Moreover, drop "BIND_DEPENDENCIES += host-pkgconf zlib" as
host-pkgconf is already mandatory

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>