ARM: dts: sam9x60ek: select PIT as tick-timer

ARM: dts: sam9x60ek: select PIT as tick-timer

U-Boot currently enables the UPLL during boot, which triggers a udelay()
call that depends on the system tick timer. Since no explicit tick source
is defined in the device tree, boot stalls on this board.

Define the "tick-timer" property under /chosen and point it to the PIT
node, ensuring U-Boot uses the PIT as the tick source.

Fixes: ac30d90f3367 ("clk: Ensure the parent clocks are enabled while reparenting")
Signed-off-by: Dharma Balasubiramani <dharma.b@microchip.com>