powerpc/5200: dts: digsy_mtc.dts: add timer0 and timer1 gpio properties

timer0 and timer1 pins are used as simple GPIO on this board.
Add gpio-controller and #gpio-cells properties to timer nodes
so that we can control gpio lines using available MPC52xx
GPT driver.

Signed-off-by: Anatolij Gustschin <agust@denx.de>