libdt: add of_property_write_string() ...

This ports the following barebox commits:

| commit 2d36433
| Author: Sascha Hauer <s.hauer@pengutronix.de>
| Date:   Thu Mar 30 10:36:58 2017 +0200
|
|     of: Add of_property_write_string()
|
|     Setting a property to a string is used many times. Create a convenience
|     function for it.
|
|     Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

| commit 4da7cf0
| Author: Ulrich Ölmann <u.oelmann@pengutronix.de>
| Date:   Fri Oct 19 06:33:11 2018 +0200
|
|     of: base: fix typo
|
|     Signed-off-by: Ulrich Ölmann <u.oelmann@pengutronix.de>
|     Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Signed-off-by: Ulrich Ölmann <u.oelmann@pengutronix.de>
Signed-off-by: Roland Hieber <rhi@pengutronix.de>

rework logging functions ...

We already use pr_* and dev_* functions. Replace some more
fprintf(stderr,...) with appropriate pr_* function calls. Also
provide control over which urgency level is printed.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

libdt: prepare to import state from barebox ...

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

libdt: sort symbols in libdt-utils.sym alphabetically ...

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

package+lib: rename dt -> dt-utils, state -> barebox-state ...

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>