le-level wakeups were not working properly.

To test, prevent CORE from going inactive/retention/off, thus
preventing the IO chain from being armed:

  # echo 3 > /debug/pm_debug/core_pwrdm/suspend

This ensures that GPIO wakeups happen via module-level wakeups and
not via IO pad.

Tested on 3430SDP using the touchscreen GPIO (gpio 2, in WKUP)
Tested on Zoom2 using the QUART interrup GPIO  (gpio 102, in PER)

Also, c.f. OMAP PM wiki for troubleshooting GPIO wakeup issues:
http://elinux.org/OMAP_Power_Management

Reported-by: Mike Chan <mikechan@google.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>