target-arm: Avoid calling arm_el_is_aa64() function for unimplemented EL It is incorrect to call arm_el_is_aa64() function for unimplemented EL. This patch fixes several attempts to do so. Signed-off-by: Sergey Sorokin <afarallax@yandex.ru> [PMM: Reworked several of the comments to be more verbose.] Reviewed-by: Peter Maydell <peter.maydell@linaro.org> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>