TI: armv7: Move ELM support to SoC configuration file.

The ELM hardware engine wihich is used for ECC error detections is not present
on OMAP3 SoC, so move the CONFIG_SPL_NAND_AM33XX_BCH from ti_armv7_common.h to
SoC configuration file.

Signed-off-by: Enric Balletbo i Serra <eballetbo@gmail.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>