drivers: soc: sunxi: add support for A64 and its SRAM C

Allwinner A64's display engine claims the SRAM C section to work.

Add support for the A64 SRAM controller and the SRAM C section of it.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>