This adds support for the NXP i.MX8MP-EVK board.

The SDRAM timings are taken from U-Boot-2020.07-rc4, other information
how to initialize the board are form U-Boot as well.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>