state: describe backend with phandle ...

We used to describe the backend with a combination of a nodepath
and partname:<name>. This is cumbersome and error prone to parse.
Instead, describe the backend with a phandle that directly points
to the partition. The resulting code is easier to read and the
devicetrees are easier to understand. Tested with both mtd and
EEPROM device, both with partitions with an offset != 0.

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

libdt: error handling: output error messages to stderr ...

Error handling in scripts cannot work correctly when error messages are
sent to stdout. Send them to stderr instead where they belong to.

To not confuse scripts by debug output, sent this type of messages to stderr as
well.

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

2nd commit ...

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