target/arm: New utility function to extract EC from syndrome

target/arm: New utility function to extract EC from syndrome

Create and use a utility function to extract the EC field
from a syndrome, rather than open-coding the shift.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20181012144235.19646-9-peter.maydell@linaro.org