Fix PKCS#11-based EdDSA support

PKCS#11-based EdDSA support in BIND is currently non-functional.

Build-time detection for PKCS#11 EdDSA support relied on the --with-eddsa option for configure being used, but that option was removed in 45abf438.
There are still some leftovers from --with-eddsa removal (git grep with-eddsa).
Commit c3b8130f removed HAVE_PKCS11_{ED25519,ED448} AC_DEFINEs from configure.ac (the values set depended on the value of the also removed --with-eddsa switch), but those macros are still the only way to enable PKCS#11-based EdDSA support in BIND.
Setting HAVE_PKCS11_ED25519 manually at compilation time causes build errors in lib/dns/pkcs11eddsa_link.c.

When the problems outlined above are alleviated, the pkcs11 system test should start mentioning "ecx" in its output (currently it only mentions "rsa" and "ecc").

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