ARM: imx7d-remarkable2: Initial device tree for reMarkable2

ARM: imx7d-remarkable2: Initial device tree for reMarkable2

The reMarkable2 (https://remarkable.com) is an e-ink tablet based on
the imx7d SoC.

This commit is based on the DTS provide by reMarkable but ported to the
latest kernel (instead of 4.14). I have removed references to
non-upstream devices and have changed the UART so that the console can
be accessed without having to open up the device via the OTG pogo pins.

Currently the kernel boots, but there is no support for the display.

WiFi is untested (no display or UART RX makes it hard to test), but
should work with the current upstream driver. As it's untested it's not
included in this commit.

Signed-off-by: Alistair Francis <alistair@alistair23.me>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>