aes: specify the required OpenSSL version
The code in the aes elements assumes OpenSSL >= 1.1.0:
- implicit library initialization;
- version retrieved with OpenSSL_version(OPENSSL_VERSION);
and it fails to build with older versions.
Specify the required OpenSSL version explicitly in meson.build so that the elements are excluded on older systems (e.g. Ubuntu 16.04) and the rest of GStreamer can still build.
BTW, supporting OpenSSL 1.0.x would not be a lot of work and I can do it if there is any interest, but for now the proposed change is enough for my use case.