pinctrl: ocelot: allow building as a module

Set PINCTRL_OCELOT config option as a tristate and add
MODULE_DEVICE_TABLE()/MODULE_LICENSE() to export appropriate
information. Moreover, switch from builtin_platform_driver()
to module_platform_driver().

Signed-off-by: Clément Léger <clement.leger@bootlin.com>
Link: https://lore.kernel.org/r/20220617103548.490092-1-clement.leger@bootlin.com


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