Remove unused symbols

This commit removes the following unused symbols:
   CONFIG_SYS_NAND_DDR_LAW
   CONFIG_SYS_NAND_ECCSTEPS
   CONFIG_SYS_NAND_ECCTOTAL
   CONFIG_SYS_NAND_ENABLE_PIN_SPL
   CONFIG_SYS_NAND_MX7_GPMI_62_ECC_BYTES
   CONFIG_SYS_NAND_U_BOOT_RELOC_SP

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>