mmc: fsl_esdhc_spl: Add support for loading proper U-Boot from unaligned location

This allows to concatenate SPL and proper U-Boot without extra alignment.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Marek Behún <kabel@kernel.org>