ARM: dts: efm32: remove skeleton.dtsi include and fix unit address warnings

Removale of skeleton.dtsi allows us also to fix the following
warning from the dts compiler:
  Warning (unit_address_vs_reg): Node /memory has a reg or ranges property, but no unit name

by adding proper unit addresses to the memory nodes. Also add missing
device_type to the memory node while at it.

Signed-off-by: Joachim Eastwood <manabian@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>