ARM: omap1: Make serial wakeup GPIOs use descriptors

The code in serial.c looks up GPIOs corresponding to a line
on the UART when muxed in as GPIO to use this as a wakeup
on serial activity for OMAP1.

Utilize the NULL device to define some board-specific
GPIO lookups and use these to immediately look up the
same GPIOs, set as input and convert to IRQ numbers,
then set these to wakeup IRQs. This is ugly but should work.

This is only needed on the OSK1 and Nokia 770 devices that
use the OMAP16xx.

Fixes: 92bf78b3 ("gpio: omap: use dynamic allocation of base")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>