cpu: Introduce a wrapper for being able to use TARGET_NAME in common code

In some spots, it would be helpful to be able to use TARGET_NAME
in common (target independent) code, too. Thus introduce a wrapper
that can be called from common code, too, just like we already
have one for target_words_bigendian().

Message-Id: <20230424160434.331175-3-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>