rockchip: rk3399: add sdram driver

Add the sdram driver for rk3399. With this patch we can boot
into depthcharge.

This patch also include a config file for lpddr3-hynix-4GB
that generated bases on its datasheet.

Please refer to TRM V0.3 Part1 Chapter 9 for DMC.

BRANCH=none
BUG=chrome-os-partner:51537
TEST=boot to depthcharge on kevin

Change-Id: I2afcaa3b68dbad77a5fe677b835289b675ed2bef
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: 5d777e29942057fb7237eefa34051d1f54b19405
Original-Change-Id: Ifa1fe98a7058869518757d50678a64620610d91d
Original-Signed-off-by: Lin Huang <hl@rock-chips.com>
Original-Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/332562
Reviewed-on: https://review.coreboot.org/14716
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
7 files changed