sunxi: Remove no longer needed default options from defconfigs

Now that those common Allwinner config symbols are defined automatically
for all boards in their Kconfig files, we can remove the now redundant
definitions from the boards' _defconfig files.

Some boards had a differing definiton for some of those symbols, it
looks like mostly to "merge races" when the symbol was introduced (new
board *_defconfig file missed the "add symbol to all files" patch).

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Tested-by: Jagan Teki <jagan@amarulasolutions.com> # Amarula A64-Relic
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>