pinctrl: Ingenic: Introduce reg_offset and use it instead hard code.

Introduce "reg_offset", use it instead hard code "0x100",
it will also be used for subsequent X1830 pinctrl driver.

Signed-off-by: 周琰杰 (Zhou Yanjie) <zhouyanjie@wanyeetech.com>
Link: https://lore.kernel.org/r/1576426864-35348-5-git-send-email-zhouyanjie@wanyeetech.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>