i.MX: Add an i.MX25 specific CCM class/instance

With this CCM, i.MX25 timer is accurate with "real world time".

Signed-off-by: Jean-Christophe Dubois <jcd@tribudubois.net>
Message-id: 2c0cf90be767bfc8520661eca891ab22c61f18fe.1449528242.git.jcd@tribudubois.net
Reviewed-by Peter Crosthwaite <crosthwaite.peter@gmail.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>