ARM: dts: imx: add devicetree for Kobo Clara HD

This adds a devicetree for the Kobo Clara HD Ebook reader. It
is on based on boards called "e60k02". It is equipped with an
imx6sll SoC.

Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>