board: verdin-imx8mp: update lpddr4 configuration and training

Update LPDDR4 configuration and training using updated spreadsheet and
tools from NXP using data from previous spreadsheet and verified
toward datasheet:
 - MX8M_Plus_LPDDR4_RPA_v9.xlsx
 - mscale_ddr_tool_v3.30.exe

From:
https://community.nxp.com/t5/i-MX-Processors-Knowledge-Base/i-MX-8M-Family-DDR-Tool-Release/ta-p/1104467



Some register values differ due to these fixes/modifications:

- corrected calculation of T_CKPDX parameter (equal to tCKCKEH for LPDDR4)
- corrected ECC related items, none of which affect normal operation
  when ECC is not enabled
- corrected formula for calculation of tRTP in cell D122

Signed-off-by: Emanuele Ghidoli <emanuele.ghidoli@toradex.com>
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>