Tested basic suspend/resume on a mx25pdk:

$ echo enabled > /sys/class/tty/ttymxc0/power/wakeup
$ echo mem > /sys/power/state

Then press any key in the serial console and the system wakes up.
Signed-off-by: NFabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: NShawn Guo <shawnguo@kernel.org>