OvmfPkg: exclude libssl functionality from OpensslLib if TLS_ENABLE=FALSE

The OpensslLibCrypto library instance (which does not contain libssl
functions) is sufficient for the Secure Boot feature.

Ease security analysis by excluding libssl functionality from the
OpensslLib instance we use with TLS_ENABLE=FALSE.

Cc: Gary Lin <glin@suse.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Tomas Hoger <thoger@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Gary Lin <glin@suse.com>