uclass: add uclass_find_device_by_phandle_id() helper

uclass: add uclass_find_device_by_phandle_id() helper

The functions uclass_find_device_by_phandle() and
uclass_get_device_by_phandle_id() both loop over a given uclass
looking for a device with a given phandle. Factor that out to a common
helper.

For now, there are no (known potential) users of the new helper
outside uclass.c, so make it static.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Reviewed-by: Simon Glass <sjg@chromium.org>
Fix warning on sandbox_spl; fix code style:
Signed-off-by: Simon Glass <sjg@chromium.org>