ARM: dts: berlin: add PPI cpu mask to twd timer interrupts

According to the gic binding document, "bits[15:8] PPI interrupt cpu
mask.  Each bit corresponds to each of the 8 possible cpus attached to
the GIC.  A bit set to '1' indicated the interrupt is wired to that
CPU." This patch wants to add the PPI cpu mask for completeness.

Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>