For more readabilty and consistency with other Broadcom SoCs, we move
all NS2 clock DT nodes from main SoC DT file to a separate DT file.

We also update the license header in ns2.dtsi as-per new Broadcom
convention.
Signed-off-by: Anup Patel <anup.patel@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>