ARM: dts: imx: Add devicetree for Tolino Vison

Add a devicetree for the Tolino Vision Ebook reader. It is based
on boards marked with "37NB-E60Q30+4A3". It is equipped with an i.MX6SL
SoC.

Expected to work:
 - Buttons
 - Wifi
 - LEDs
 - uSD
 - eMMC
 - USB
 - RTC
 - Touchscreen
 - Backlight

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