ARM: mxs: Add support for the eukrea-cpuimx28.

The following devices/functionalities were tested:
 * Main UART.
 * Ethernet0.
 * Ethernet1.
 * SD.
 * USB host.
 * USB otg.
 * Display(and its backlight).
 * Touchscreen.
 * Audio.
 * nand.
 * i2c and the pcf8563 device.
 * The gpio buttons.
 * The gpio leds.
 * Watchdog

Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: devicetree@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Eric Bénard <eric@eukrea.com>
Signed-off-by: Denis Carikli <denis@eukrea.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>