Add the initial support for imx7d-pico board.

Add support for eMMC, USB host, USB device, PMIC, Ethernet and audio.

For more information about this board, please visit:
http://www.technexion.org/products/pico/pico-som/pico-imx7-emmcSigned-off-by: NVanessa Maegima <vanessa.maegima@nxp.com>
Reviewed-by: NFabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: NShawn Guo <shawnguo@kernel.org>