clk: armada-37xx: Support soc_clk_dump

Add support for the clk dump command on Armada 37xx.

Signed-off-by: Marek Behun <marek.behun@nic.cz>
Reviewed-by: Stefan Roese <sr@denx.de>
Signed-off-by: Stefan Roese <sr@denx.de>