sunxi: configs: merge sun9i and sun50i SPL memory definitions

sunxi: configs: merge sun9i and sun50i SPL memory definitions

For some reason we were pretty conservative when defining the maximum
SPL size for the Allwinner A80(sun9i) SoC.
According to the manual the SRAM A1 is even 40KB, but the BROM
probably still has the 32 KiB load limit. For the sake of simplicity,
merge the SPL memory definitions for the A64 and A80 SoCs, since both
SoC share the BROM/SRAM A1 memory layout.
This helps to further simplify this is in the next patch.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>