sunxi: board: annotate #endif lines

The legacy Allwinner code is cluttered with #ifdef's, some of them even
nested, which makes the code hard to read and error prone.
Eventually we will get rid of most of them, but for now let's at least
annotate the #endif lines with the corresponding symbol the bracket
started with.

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