arm64: dts: Add ARM PMUv3 DT node in NS2 DT

The NS2 SoC has Cortex-A57 CPUs which support ARM PMUv3 so,
lets enable ARM PMUv3 in NS2 DT.

Signed-off-by: Anup Patel <anup.patel@broadcom.com>
Reviewed-by: Vikram Prakash <vikramp@broadcom.com>
Reviewed-by: Ray Jui <rjui@broadcom.com>
Reviewed-by: Scott Branden <sbranden@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>