Revert "package/rtty: remove unnecessary cmake options"

Revert "package/rtty: remove unnecessary cmake options"

This reverts commit 7f169e6bc3812d7f9160449d7724711e4df7e39e.

As pointed out by Yann E. Morin, we really want to explicitly disable
crypto backends, otherwise they will get automatically re-enabled if
one of the dependencies is found:

    elseif(OPENSSL_FOUND)
        set(RTTY_USE_OPENSSL ON)
    elseif(WOLFSSL_FOUND)
        set(RTTY_USE_WOLFSSL ON)
    elseif(MBEDTLS_FOUND)
        set(RTTY_USE_MBEDTLS ON)

But as usual, dependencies may incorrectly be found, so we want to
explicitly disable.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>