sunxi_nand_spl: Remove NAND_SUNXI_SPL_SYNDROME_PARTITIONS_END

sunxi_nand_spl: Remove NAND_SUNXI_SPL_SYNDROME_PARTITIONS_END

We only ever use syndrome mode for the partitions which contain the SPL,
as that is required for the BROM to be able to read the SPL.

Instead of using some arbritray limit for deciding whether or not to
use syndrome, be smart and check if u-boot-dtb.bin is directly behind
the SPL, if it is not then it is on its own partition and we should not
use syndrome.

Note the reason why we only use syndrome mode for the SPL is because it
comeswith weaker randomization, introducing a risk for more bit errors,
so we want to avoid it when possible.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>