ARM: rockchip: Constify struct regmap_config and staticize local function

The regmap_config struct may be const because it is not modified by the
driver and regmap_init() accepts pointer to const.

Make function rockchip_get_core_reset() static because it is not used
outside of the platsmp.c file.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>