board: apalis_imx6: DDR init using mx6_dram_cfg()

board: apalis_imx6: DDR init using mx6_dram_cfg()

Do DDR initialization using the procedural mx6_dram_cfg() instead of
programming the MMDC using a raw list of register/value pairs, this
solves some rare boot failures on specific "bad" modules.

Calibration values, DDR geometry are unchanged, memory timings are
updated according to the relevant memory datasheet, no changes on
the power consumption.

For IT temperature range SKUs CL is decreased from 8 to 7 and tFAW
value is increased, for commercial temperature range SKUs some
changes on ODT parameters.

This change was validated over a range of different apalis-imx6 SoM, on
the whole working temperature range with weeks of continuous testing.

Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Reviewed-by: Fabio Estevam <festevam@denx.de>
Acked-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>