ARM: dts: at91: vinco: use TCB2 as timers

As TCB2 doesn't have any output pins, use it for timers

Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>