arm: mx6: Add CCV xPress board support

This patch add support for the CCV xPress board which is equipped
with the i.MX6UL. And provides the following interfaces:

- 128MiB DDR
- UART
- I2C
- eMMC (with booting)
- Ethernet
- USB

This patch adds two build targets. One with and one without SPL. The
non-SPL version is used for loading U-Boot via USB (imx_usb_loader).

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>