Input: ti_am335x_tsc - prevent system suspend when TSC is in use

Prevent system suspend while user has finger on touch screen,
because TSC is wakeup source and suspending device while in use will
result in failure to disable the module.
This patch uses pm_stay_awake() and pm_relax() APIs to prevent and
resume system suspend as required.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Vignesh R <vigneshr@ti.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>