dm: core: add internal functions for getting the device without probe

This commit extends the uclass-internal functions by:
- uclass_find_first_device()
- uclass_find_next_device()
For both functions, the returned device is not probed.

After some cleanup, the above functions are called by:
- uclass_first_device()
- uclass_next_device()
for which, the returned device is probed.

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Cc: Simon Glass <sjg@chromium.org>
Acked-by: Simon Glass <sjg@chromium.org>