If the touchscreen is configured as wakeup source we should not be cutting
off power to it.

Also, now that the driver relies on I2C client to supply IRQ, we do not
need to explicitly enable and disable IRQ for wakeup: if device is created
as wakeup source, I2C core will mark interrupt as wakeup one.
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>