Input: egalax_ts - add system wakeup support

This patch adds wakeup function support for egalax touch
screen, if "wakeup-source" is added to device tree's egalax
touch screen node, the wakeup function will be enabled, and
egalax touch screen will be able to wakeup system from suspend.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>