pinctrl: dove: Constify struct regmap_config and of_device_id

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

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>