Instead of hardcoding 16 various places in the code, use a define to
make it more clear what is going on.
Signed-off-by: NChristoffer Dall <christoffer.dall@linaro.org>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>