ARM: dts: berlin: enable timer 1 for sched_clock

Enable timer 1 to be the source for the sched_clock, allowing to have a
more precise value than 1/HZ.

Signed-off-by: Antoine Ténart <antoine.tenart@free-electrons.com>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>