pinctrl: ingenic: Rename registers from JZ4760_GPIO_* to JZ4770_GPIO_*

Now that JZ4760 support has been fixed, it looks wrong to have
JZ4760_GPIO_* registers being written if the SoC is a JZ4770 or later.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20201211232810.261565-2-paul@crapouillou.net
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>