arm64: dts: Add clock DT nodes for Stingray SOC

This patch describes Stingray SOC clock tree using
DT nodes in Stingray DTS.

Signed-off-by: Sandeep Tripathy <sandeep.tripathy@broadcom.com>
Reviewed-by: Ray Jui <ray.jui@broadcom.com>
Reviewed-by: Scott Branden <scott.branden@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>