target-arm: convert check_ap to ap_to_rw_prot

Instead of mixing access permission checking with access permissions
to page protection flags translation, just do the translation, and
leave it to the caller to check the protection flags against the access
type. Also rename to ap_to_rw_prot to better describe the new behavior.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1426099139-14463-2-git-send-email-drjones@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
