input: add suspend wakeup support to sh_keysc

This patch adds wakeup support to the sh_keysc driver.
With this feature the ".../power/wakeup" file can be
used to enable and disable if the device takes the
system out of suspend. Default is enabled.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>