target/arm: Pass in current_el to fp and sve_exception_el

We are going to want to determine whether sve is enabled
for EL other than current.

Tested-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20181005175350.30752-4-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>