soc: sunxi: sram: Constify struct regmap_config

`sunxi_sram_regmap_config` is not modified and can be declared as const
to move its data to a read-only section.

Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Link: https://lore.kernel.org/r/20240705-sunxi-sram-const-regmap_config-v1-1-1b997cd65d0f@gmail.com


Signed-off-by: Chen-Yu Tsai <wens@csie.org>