curl: configure with '--without-ssl' if ssl is disabled

curl requires that at least one SSL implementation or explicitly
'--without-ssl' is specified. This is particularly the case if
PACKAGECONFIG is empty.

| configure: error: select TLS backend(s) or disable TLS with
--without-ssl.
|
| Select from these:
|
|   --with-amissl
|   --with-bearssl
|   --with-gnutls
|   --with-mbedtls
|   --with-mesalink
|   --with-nss
|   --with-openssl (also works for BoringSSL and libressl)
|   --with-rustls
|   --with-schannel
|   --with-secure-transport
|   --with-wolfssl
|

Fixes: eef6c45f ("curl: Rework openssl and random PACKAGECONFIGs")
Signed-off-by: Christian Eggers <ceggers@arri.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>