pinctrl: pinctrl-loongson2: fix Kconfig dependency

pinctrl: pinctrl-loongson2: fix Kconfig dependency

If CONFIG_PINCTRL_LOONGSON2=y and CONFIG_OF is not set,
gcc complained about undefined reference:

drivers/pinctrl/pinctrl-loongson2.o: In function `pinconf_generic_dt_node_to_map_all':
pinctrl-loongson2.c:(.text+0x1c4): undefined reference to
`pinconf_generic_dt_node_to_map'

To fix this error, add depends on OF to
config PINCTRL_LOONGSON2.

Fixes: f73f88acbc18 ("pinctrl: pinctrl-loongson2: add pinctrl driver support")
Signed-off-by: Ren Zhijie <renzhijie2@huawei.com>
Link: https://lore.kernel.org/r/20221121132608.230645-1-renzhijie2@huawei.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>