ARM: dts: NSP: Fix PPI interrupt types

Booting a kernel results in the kernel warning us about the following
PPI interrupts configuration:
[    0.105127] smp: Bringing up secondary CPUs ...
[    0.110545] GIC: PPI11 is secure or misconfigured
[    0.110551] GIC: PPI13 is secure or misconfigured

Fix this by using the appropriate edge configuration for PPI11 and
PPI13, this is similar to what was fixed for Northstar (BCM5301X) in
commit 0e34079c ("ARM: dts: BCM5301X: Correct GIC_PPI interrupt
flags").

Fixes: 7b2e987d ("ARM: NSP: add minimal Northstar Plus device tree")
Fixes: 1a9d53ca

 ("ARM: dts: NSP: Add TWD Support to DT")
Acked-by: Jon Mason <jon.mason@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>