dm: core: uclass: add function: uclass_find_device_by_name()

This commit extends the driver model uclass's API by function:
- uclass_find_device_by_name()

And this function returns the device if:
- uclass with given ID, exists,
- device with exactly given name(dev->name), exists.

The returned device is not activated - need to be probed before use.

Note:
This function returns the first device, which name is equal
to the given one. This means, that using this function you must
assume, that the device name is unique in the given uclass's ID
device list.

uclass-internal.h: cleanup - move the uclass_find_device_by_seq()
declaration and description, near the other uclass_find*() functions.

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