This patch provides the code to calibrate the DDR's
DQS to DQ signals (RDLVL).
It is based on:
VFxxx Controller Reference Manual, Rev. 0, 10/2016, page 1600
10.1.6.16.4.1 "Software Read Leveling in MC Evaluation Mode"
and NXP's community thread:
"Vybrid: About DDR leveling feature on DDRMC."
https://community.nxp.com/thread/395323
Signed-off-by: Lukasz Majewski <lukma@denx.de>
