ddr: imx93: update the ddr init to support mult setpoints

Update the DDR init flow for multi-setpoint support on i.MX93. A new
fsp_cfg struct need to be added in the timing file to store the diff
part of the DDRC and DRAM MR register for each setpoint.

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Reviewed-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>