ARM: dts: Add LEGO MINDSTORMS EV3 dts

This adds a device tree definition file for LEGO MINDSTORMS EV3.

What is working:

* Pin muxing
* Pinconf
* GPIOs
* MicroSD card reader
* UART on input port 1
* Buttons
* LEDs
* Poweroff/reset
* Flash memory
* EEPROM
* USB host port
* USB peripheral port

What is not working/to be added later:

* Speaker - have patch submitted to get pwm-beeper working - maybe someday
  it will have a real sound driver that uses PRU
* A/DC chip - have driver submitted and accepted - waiting for ack on
  device tree bindings
* Display - waiting for "simple DRM" to be mainlined
* Bluetooth - needs new driver for sequencing power/enable/clock
* Input and output ports - need some sort of new phy or extcon driver as
  well as PRU UART and PRU I2C drivers
* Battery indication - needs new power supply driver

Note on flash partitions:

These partitions are based on the official EV3 firmware from LEGO. It is
expected that most users of the mainline kernel on EV3 will be booting from
an SD card while retaining the official firmware in the flash memory.
Furthermore, the official firmware uses an ancient U-Boot (2009) that has
no device tree support. So, it makes sense to have this partition table in
the EV3 device tree file. In the unlikely case that anyone does create
their own firmware image with different partitioning, they can use a modern
U-Boot in their own firmware image that modifies the device tree with the
custom partitions.

Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>