This callback is unused by the serial core since pre-git days
and is not coming back. Delete it. Enabling wakeup on the
SA1100 platforms should be done in the suspend() callback
so the platform hook is left in the serial port struct for
later enablement.

Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>