ARM: dts: vf610: fix IRQ flag of global timer

The global timer IRQ (PPI[0], PPI 11 in device tree terms) is a
rising edge interrupt. The ARM Cortex-A5 MPCore TRM in Chapter
10.1.2. Interrupt types and sources says:
"Interrupt is rising-edge sensitive."

The bits seem to be read-only, hence this missconfiguration had
no negative effect. However, with commit 992345a5
("irqchip/gic: WARN if setting the interrupt type for a PPI fails")
warnings such as this get printed:
GIC: PPI11 is secure or misconfigured

With this change the new configuration matches the default
configuration and no warning is printed anymore.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>