The spec[1] says that top level memory nodes `shall have device_type =
"memory"'. Since 8226f7f9 ("of: base: parse all available memory nodes"),
we parse only nodes with device_type = "memory", so we should add the
device_type property where ever it's missing. When the nodes were first
added, this wasn't an issue because the skeleton.dtsi defined a memory
skeleton with correct device_type, but this was removed upstream and
imported into barebox along with 1dc748b3 ("dts: update to v5.1-rc1").

Upstream device trees with a memory node were adapted to have
device_type = "memory" in-line. This wasn't the case for nodes defined
only within barebox. Rectify this now and rename the nodes to feature a
unit name as well to be aligned with the upstream trend.

[1]: https://github.com/devicetree-org/devicetree-specification/releases/download/v0.3/devicetree-specification-v0.3.pdf

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>