sunxi: mmc: group non-DM specific functions

sunxi: mmc: group non-DM specific functions

As the SPL code for sunxi boards does not use the driver model, we have
two mmc_ops structures, one for DM, one for non-DM. The actual hardware
access code is shared, with the respective callback functions using that
common code.

To make this more obvious and easier to read, reorder the functions to
group them: we first have the common code, then the non-DM bits, and
the proper DM implementation at the end.
Also document this structure in the comment at the beginning of the file.

No functional change intended.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Samuel Holland <samuel@sholland.org>
Tested-by: Samuel Holland <samuel@sholland.org>