cmd: clk: Add trivial implementation of clock dump for DM

cmd: clk: Add trivial implementation of clock dump for DM

Add trivial implementation of the clk dump in case DM is enabled.
This implementation just iterates over all the clock registered
with the CLK uclass and prints their rate.

Signed-off-by: Marek Vasut <[email protected]>
Cc: Chin Liang See <[email protected]>
Cc: Dinh Nguyen <[email protected]>
Cc: Ley Foon Tan <[email protected]>
Cc: Simon Glass <[email protected]>
Cc: Tom Rini <[email protected]>
Reviewed-by: Ley Foon Tan <[email protected]>