OMAP2/3/4: UART: Allow per-UART disabling wakeup for serial ports

This patch causes the OMAP uarts to honor the sysfs power/wakeup file
for IOPAD wakeups. Before the OMAP was always woken up from off mode
on a rs232 signal change.  This patch also creates a different
platform device for each serial port so that the wakeup properties can
be control per port.

By default, IOPAD wakeups are enabled for each UART.  To disable,

  # echo disabled > /sys/devices/platform/serial8250.0/power/wakeup

Where serial8250.0 can be replaced by .1, or .2 to control the other
ports.

Original idea and original patch from Russ Dill <russ.dill@gmail.com>

Cc: Russ Dill <russ.dill@gmail.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>