clk: Get the CLK by index without device

Getting a CLK by index with device is not straight forward
for some use-cases like handling clock operations for child
node in parent driver. So we need to process the child node
in parent probe via ofnode and process CLK operation for child
without udevice but with ofnode.

So add clk_get_by_index_nodev() and move the common code
in clk_get_by_index_tail() to use for clk_get_by_index()

Cc: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Simon Glass <sjg@chromium.org>