Target unicore32 was deprecated in commit 8e4ff4a8, v5.2.0.  See
there for rationale.

Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20210503084034.3804963-3-armbru@redhat.com>
Acked-by: Thomas Huth <thuth@redhat.com>