OMAP3: Move secure_unlock() function to not duplicate code

OMAP3: Move secure_unlock() function to not duplicate code

The secure_unlock() function is implemented by various boards, this
patch moves this function to a common place to not duplicate code.

 board/omap3530beagle/omap3530beagle.c :527:void secure_unlock(void)
 board/igep00x0/igep00x0.c             :271:void secure_unlock(void)
 board/omap3430sdp/omap3430sdp.c       :314:void secure_unlock(void)
 board/omap3evm/omap3evm.c             :359:void secure_unlock(void)
 board/omap3430labrador/omap3430sdp.c  :316:void secure_unlock(void)
 board/overo/overo.c                   :478:void secure_unlock(void)

Signed-off-by: Enric Balletbo i Serra <eballetbo@gmail.com>
Signed-off-by: Anand Gadiyar <gadiyar@ti.com>