This code is becoming duplicated in many places.  So let's consolidate
it into a handy macro that is known to be right and available for reuse.
Signed-off-by: NNicolas Pitre <nico@linaro.org>
Acked-by: NDave Martin <Dave.Martin@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>