pinctrl: rk805: Constify rk805_gpio_cfgs

Mark pin_cfg as const, allowing the compiler to put the struct in
.rodata instead of .data.

Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Link: https://lore.kernel.org/r/20200425203813.6442-1-rikard.falkeborn@gmail.com


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