ARM: dts: imx50-kobo-aura: Add Netronix embedded controller

Enable the Netronix EC on the Kobo Aura ebook reader.

Several features are still missing:
 - Frontlight/backlight. The vendor kernel drives the frontlight LED
   using the PWM output of the EC and an additional boost pin that
   increases the brightness.
 - Battery monitoring
 - Interrupts for RTC alarm and low-battery events

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>