ARM: dts: BCM5301X: Correct GIC_PPI interrupt flags

GIC_PPI flags were misconfigured for the timers, resulting in errors
like:
[    0.000000] GIC: PPI11 is secure or misconfigured

Changing them to being edge triggered corrects the issue

Suggested-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Jon Mason <jon.mason@broadcom.com>
Fixes: d27509f1

 ("ARM: BCM5301X: add dts files for BCM4708 SoC")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>