dm: clk: Define clk_get_by_id() for clk operations

dm: clk: Define clk_get_by_id() for clk operations

This commit adds the clk_get_by_id() function, which is responsible
for getting the udevice with matching clk->id. Such approach allows
re-usage of inherit DM list relationship for the same class (UCLASS_CLK).
As a result - we don't need any other external list - it is just enough
to look for UCLASS_CLK related udevices.

Signed-off-by: Lukasz Majewski <lukma@denx.de>
Reviewed-by: Peng Fan <peng.fan@nxp.com>