boards: Add support for WaRP7 board

This patch is to add support for the WaRP7 board which has an i.MX7
Solo SoC.
The Zephyr is running on the Cortex M4 core and the following features
were validated on this board:

* GPIO: User Switch detection and sensors interrupt
* UART: Zephyr console
* I2C: Communication with fxos8700 and fxas21002 sensors

Signed-off-by: Diego Sueiro <diego.sueiro@gmail.com>